This set of *Physics problems for class 9 *students of CBSE/ICSE/HS boards cover Newton’s Laws of motion, Force, linear motion equations – kinematics, motion class 9 numericals and Gravitation (gravitational force). It covers vertical upward movement problems as well.

***Questions starting from 47 cover harder problems on *motion under gravity. Also added problems on Pressure, Buoyant force and Buoyancy and conservation of momentum.

All these are apt for class 9 ICSE and CBSE boards.

**In problems starting from *61*, you will find new set of problems on kinematics and motion, a new set on simple pendulum, few interesting problems on relative density.

New problems on mirror (light) are added Q86 onwards.

I hope our readers & students will like this set and try to solve the numerical problems themselves.

*Now get the solutions as well* (for most), but you should try yourself every physics problem first.

The difficulty level is medium for most of the numericals. Surely these *Physics problems for class 9* – set 1 will help to test your basics. We have also published a second set on force and laws of motion. You can read it here: class 9 numericals – set 2

These problems not only help the students of high school but also help many to face diverse competitive examinations. Let’s start with numerical problems on the motion for class 9 with the solution.

## Physics problems for class 9- set 1 (101 Qs) – with solution & links (CBSE /ICSE)

** 101 Numeric problems** – important question physics

** CBSE 9th physics motion problems with solution **

**1) A force of 1000 Newton is applied on a 25 kg mass for 5 seconds. What would be its velocity?**

[ Solution: Click here for the solution of Q1]

**2) A force is applied to a mass of 16 kg for 3 seconds. As the force is removed the mass moves 81 meters in 3 seconds. What was the value of the force applied?**

[ Solution: Click here for the solution of Q2]

** 3) A mass of 50 kg was moving with a velocity of 400 m/s. A force of 40000 N is applied to the mass and its velocity is reduced to 50 m/s after some time. What is the distance traveled by the mass during this period?**Click here for the solution of Q3]

[ Solution:

**4) A ball of 150 g mass moves with 12 m/s and bounces back after hitting a wall with 20 m/s after a small duration of 0.01 second. What was the force applied to the ball when it hits the wall?**

[ Solution: Click here for the solution of Q4]

** 5) Momentum of an object changes from 100 kg m/s to 200 kg m/s in 2 seconds. What is the force applied to it?**Click here for the solution of Q5]

[ Solution:

## physics numerical for class 9

**6) A force of 200 N is applied on a body and its velocity changes from 5m/s to 10m/s in a second. What is the mass of the body?**

[ Solution: Click here for the solution of Q6]

** 7) A mass of 1 kg is moving from east to west with a velocity of 10 m/s. A force is applied on it for 2 seconds and its velocity becomes 5 m/s. What is the value and direction of the force?**Click here for the solution of Q7]

[ Solution:

## solved numerical problems on gravitation for class 9

**8) If the distance between 2 objects is doubled then how will the gravitational force between them change?**

[ Solution: Click here for the solution of Q8]

**9) If the distance between 2 objects is halved then how will the gravitational force between them change?**

[ Solution: Click here for the solution of Q9]

**10) If the masses of the 2 objects are doubled then how will the gravitational force between them change?**

[ Solution: Click here for the solution of Q10]

## physics numerical for class 9

** 11) A force acts for 10 s on a stationary body of mass 100 kg after which the force ceases to act. The body moves through a distance of 100 m in the next 5 s. Calculate (i) the velocity acquired by the body, (ii) the acceleration produced by the force, and (iii) the magnitude of the force. **

**[ Solution: click this link for solution Q11 ]**

CBSE class 9 **Physics problems – physics numerical**

**12) A force acts for 0.1 sec on a body of mass 2 kg initially at rest. The force is then withdrawn and the body moves with a velocity of 2 m/s. Find the magnitude of the force. ****Solution: click this link for solution Q12 **

** 13) A cricket ball of mass 100 g moving at a speed of 30 m/s is brought to rest by a player in 0.03 s. find the average force applied by the player. **** Solution: click this link for solution Q13**

## Physics problems – motion class 9 numericals

**14) A body of mass 500 g, initially at rest, is acted upon by a force which causes it to move a distance of 4 m in 2 sec. Calculate the force applied. **** Solution: click this link for solution Q14**

**15) A force causes an acceleration of 10 m/s^2 in a body of mass 500 g. What acceleration would be caused by the same force in a body of mass 5 kg. **

**Solution: click this link for solution Q15 **

** 16) A bullet of mass 50 g moving with an initial velocity of 100 m/s, strikes a wooden block and comes to rest after penetrating a distance 2 cm in it. Calculate: (i) Initial momentum of the bullet (ii)final momentum of the bullet (iii) retardation caused by the wooden block, and (iv) resistive force exerted by the wooden block **

**Solution: click this link for solution Q16**

## Physics problems – important question physics

**17) From the velocity-time graph, find out the distance traveled in each section A, B, C and D. Also find the total distance traveled.**

** ****Solution: click this link for solution Q17**

**18) A car starts from rest and accelerates uniformly over a time of 7 seconds for a distance of 98 m. Determine the acceleration of the car.**

**Solution: click this link for solution Q18**

## CBSE 9th physics motion problems with solution

**19) A car traveling at 20 m/s skids to a stop in 3 s. Determine the skidding distance of the car (assume uniform acceleration).**

**Solution: click this link for solution Q**19

**20) An airplane accelerates down a runway at 4 m/s**^{2}** for 30s until is finally lifts off the ground. Determine the distance traveled before takeoff.**

**Solution: click this link for solution Q**20

## motion class 9 numericals- CBSE, icse, board

**21) A feather is dropped on the moon from a height of 10 meters. The acceleration of gravity on the moon is one-sixth of that on the earth. Determine the time for the feather to fall to the surface of the moon.**

**Solution: click this link for solution Q** 21

**22) If a rocket-powered sled is accelerated to a speed of 400 m/s in 2 seconds, then what is the acceleration and what is the distance that the sled travels?**

**Solution: click this link for solution Q**22

## Physics problems for class 9 continued, CBSE, icse, board

**23) An engineer is designing the runway for an airport. Of the planes that will use the airport, the lowest acceleration rate is likely to be 3 m/s**^{2}**. The takeoff speed for this plane will be 65 m/s. Assuming this minimum acceleration, what is the minimum allowed length for the runway?**

**Solution: click this link for solution Q 23**

**24) Upton Chuck is riding the Giant Drop at Great America. If Upton free falls for 2.60 seconds, what will be his final velocity and how far will he fall?**

**Solution: click this link for solution Q** 24

**25) A bike accelerates uniformly from rest to a speed of 10 m/s over a distance of 30 m. Determine the acceleration of the bike.**

**Solution: click this link for solution Q25**

**26) A race car accelerates uniformly from 25 m/s to 50 m/s in 5 seconds. Determine the acceleration of the car and the distance traveled.**

**Solution: click this link for solution Q 26**

## Physics problems for class 9.. continued, cbse, icse, board

**27) A bullet leaves a rifle with a muzzle velocity of 600 m/s. While accelerating through the barrel of the rifle, the bullet moves a distance of 0.8 m. Determine the acceleration of the bullet (assume a uniform acceleration).**

**Solution: click this link for solution Q 27**

**28) A bullet is moving at a speed of 350 m/s when it embeds into a lump of moist clay. The bullet penetrates for a distance of 0.05 m. Determine the acceleration of the bullet while moving into the clay. (Assume a uniform acceleration.)**

**Solution: click this link for solution Q 28**

## physics numericals for class 9

**29) A plane has a takeoff speed of 100 m/s and requires 1500 m to reach that speed. Determine the acceleration of the plane and the time required to reach this speed.**

**Solution: click this link for solution Q**29

**30)A baseball is popped straight up into the air and has a hang-time of 6 s. Determine the height to which the ball rises before it reaches its peak. (Hint: the time to rise to the max height is one-half the total hang-time.)**

**Solution: click this link for solution Q30 **

##### Physics problems for class 9.. continued, cbse, icse, board

**31) If a box is pushed horizontally on the floor with a force of 10 N and it moves 5 meter along the line of action of the force, then what is the work done by the Gravity or earth’s gravitational pull on that box ?**

**Solution: click this link for solution Q31**

##### cbse 9th physics motion problems with solution

**32) A train is moving at a velocity of 25 ms-1. It is brought to rest by applying the brakes which produce uniform retardation of 0.5 ms-2. Calculate (i) the velocity of the train after 10 s (ii) If the mass of the train is 20000 kg then calculate the force required to stop the train **

**Solution: click this link for solution Q3**2

**33) A spring balance is used to find the weight of a body X on the surface of the moon. The mass of the body X is 2 kg and its weight is recorded as 3.4 N. The weight of another body Y recorded by the same balance is found to be 7.65 N. Calculate the mass of the body Y.**

**Solution: click this link for solution Q3**3

## solved numericals on gravitation – gravitation problems class 9 cbse

**34) Calculate the force of gravitation between two objects of masses 50 kg and 120 kg respectively kept at a distance of 10 m from one another. (Gravitational constant, ****G ****= 6.7 × ** 10 ^{-11}** ** **Nm^2/kg^2** **)**

**Solution: click this link for solution Q34**

**35) What is the force of gravity on a body of mass 150 kg lying on the surface of the earth?(Mass of earth = 6 × 10^24 kg; Radius of earth = 6.4 × 10^6 m; **

**G****= 6.7 ×**10

^{-11}

**Nm^2/kg^2)**

**Solution: click this link for solution Q35**

**36) The mass of sun is 2 × 10^30 kg and the mass of earth is 6 × 10^24 kg. If the average distance between the sun and the earth be 1.5 × 10^8 km, calculate the force of gravitation between them.**

**Solution: click this link for solution Q36**

**37) A piece of stone is thrown vertically upwards. It reaches the maximum height in 3 seconds. If the acceleration of the stone is 9.8 m/s^2 directed towards the ground, calculate the initial velocity of the stone with which it is thrown upwards.**

**Solution: click this link for solution Q37**

## icse problems for class 9 physics – physics question

**38) A stone falls from a building and reaches the ground 2.5 seconds later. How high is the building ? (****g ****= 9.8 m/s^2)**

**Solution: click this link for solution Q3**8

**39) A stone is dropped from a height of 20 m.(****i****) How long will it take to reach the ground?(****ii****) What will be its speed when it hits the ground? (****g ****= 10 m/s^2)**

**Solution: click this link for solution Q3**9

##### numericals on equation of motion for class 9

**40) A stone is thrown vertically upwards with a speed of 20 m/s. How high will it go before it begins to fall? (****g ****= 9.8 m/s^2)**

**Solution: click this link for solution Q**40

**41) When a cricket ball is thrown vertically upwards, it reaches a maximum height of 5 metres.(****a****) What was the initial speed of the ball ?(****b****) How much time is taken by the ball to reach the highest point ? (****g ****=10 m/ s^2)**

**Solution: click this link for solution Q**41

**42) A force of 20 N acts upon a body whose weight is 9.8 N. What is the mass of the body and how much is its acceleration? (****g ****= 9.8 m/ s^2).**

**Solution: click this link for solution Q42**

**43) A stone resting on the ground has a gravitational force of 20 N acting on it. What is the weight of the stone? What is its mass ? ( ****g ****= 10 m/s^2).**

**Solution: click this link for solution Q43**

## gravitation problems physics

**44)****(a) An object has a mass of 20 kg on earth. ****What will be its (****i****) mass, and (****ii****) weight, on the moon ?(****g ****on moon = 1.6 m/s^2).****(****b****) Calculate the acceleration due to gravity on the surface of a satellite having a mass of 7.4 × 10^22 kg and a radius of 1.74 × 10^6 m (****G ****= 6.7 × ** 10 ^{-11}** Nm^2/kg^2). **

**Solution: click this link for solution Q44**

**45) The mass of a planet is 6 × 10^24 kg and its diameter is 12.8 × 10^3 km. If the value of the gravitational constant is 6.7 × ** 10 ^{-11}** Nm2/kg2, calculate the value of acceleration due to gravity on the surface of the planet. **

**Solution: click this link for solution Q45**

##### icse problems for class 9 physics – physics question

**46) The values of ****g ****at six distances A, B, C, D, E and F from the surface of the earth are found to be 3.08 m/s^2, 9.23 m/s^2, 0.57 m/s^2, 7.34 m/s^2, 0.30 m/s^2 and 1.49 m/s^2, respectively. ****(****a****) Arrange these values of ****g ****according to the increasing distances from the surface of the earth (keeping the value of ****g ****nearest to the surface of the earth first) ****(****b****) If the value of distance F be 10000 km from the surface of the earth(****hint: check if possible or not****), state whether this distance is deep inside the earth or high up in the sky. Give the reason for your answer of the place of observation**

**Solution: click this link for solution Q4**6

**47) A pebble is dropped freely in a well from its top. It takes 20 s for the pebble to reach the water surface in the well. Taking ****g ****= 10 m/s^2 and speed of sound = 330 m/s, find: (i) the depth of water surface, and (ii) the time when echo is heard after the pebble is dropped. **

**[answer Hint: 2000 m ; 26.06 secs ]

**Solution: click this link for solution Q4**7

## cbse problems for class 9 physics – motion under gravity

**48) A ball is thrown vertically upwards from the top of a tower with an initial velocity of 19·6 m/s. The ball reaches the ground after 5 s. Calculate: (i) the height of the tower, (ii) the velocity of ball on reaching the ground. Take ****g ****= 9·8 m/s^2**

**[answer Hint: 24.5 m ; 29.4 m/s ]

**Solution: click this link for solution Q4**8

**49) A hammer exerts a force of 1·5 N on each of the two nails ****A ****and ****B. ****The area of cross-section of tip of nail ****A ****is 2 mm^2 while that of nail ****B ****is 6 mm^2. Calculate pressure on each nail in pascal.**

**Solution: click this link for solution Q4**9

**50) A block of iron of mass 7·5 kg and of dimensions 12 cm x 8 cm x 10 cm is kept on a table top on its base of side 12 cm x 8 cm. Calculate: (a) thrust and (b) pressure exerted on the tabletop. Take 1 kgf=10 N. **

**Solution: click this link for solution Q50**

**51) A vessel contains water up to a height of 1·5 m. Taking the density of water 1()^3 kg /m^3, acceleration due to gravity 9·8 m/ S^2 and area of the base of vessel 100 cm^2, calculate: (a) the pressure and (b) the thrust, at the base of the vessel. **

**Solution: click this link for solution Q51**

## Pressure problem – cbse, icse

**52) The area of base of a cylindrical vessel is 300 cm^2. Water (density = 1000 kg /m^3) is poured into it up to a depth of 6 cm. Calculate: (a) the pressure and (b) the thrust of water on the base. ****(g ****= 10 m/ s^2).**

**Solution: click this link for solution Q52**

**53)Calculate the height of a water column which will exert on its base the same pressure as the 70 cm column of mercury. Density of mercury is 13.6 g/cm^3.**

**Solution: click this link for solution Q5**3

**54) A boy of mass 50 kg running at 5 m/s jumps on to a 20 kg trolley traveling in the same direction at 1.5 m/s. What is their common velocity ?**

**Solution: click this link for solution Q54**

##### momentum conservation – physics numericals

**55) A girl of mass 50 kg jumps out of a rowing boat of mass 300 kg on to the bank, with a horizontal velocity of 3 m/s. With what velocity does the boat begin to move backward?**

**Solution: click this link for solution Q5**5

**56)A truck of mass 500 kg moving at 4 m/s collides with another truck of mass 1500 kg moving in the same direction at 2 m/s. What is their common velocity just after the collision if they move off together?**

**Solution: click this link for solution Q5**6

## numericals of motion class 9

**57) A ball ****X ****of mass 1 kg traveling at 2 m/s has a head-on collision with an identical ball ****Y ****at rest. ****X ****stops and ****Y ****moves off. Calculate the velocity of ****Y ****after the collision.**

**Solution: click this link for solution Q57 **

**58) A heavy car A of mass 2000 kg traveling at 10 m/s has a head-on collision with a sports car B of mass 500 kg. If both cars stop dead on colliding, what was the velocity of car B ?**

**Solution: click this link for solution Q58**

##### physics numericals

**59) A man wearing a bullet-proof vest stands still on roller skates. The total mass is 80 kg. A bullet of mass 20 grams is fired at 400 m/s. It is stopped by the vest and falls to the ground. What is then the velocity of the man?**

**Solution: click this link for solution Q59**

**60) A metallic sphere of mass 2 kg and volume 2.5 x 10**^{-4}** ** m^{3}** is completely immersed in water. Find the buoyant force exerted by water on the sphere. Density of water = 1000 kg/m**^{3}

**Solution: click this link for solution Q60**

## pendulum problems

61) Two simple pendulums *A *and *B *have equal length, but their bobs weigh 50 gf and l00 gf respectively. What would be the ratio of their time periods ? Give a reason for your answer.

**Solution: click this link for solution Q61 **

62) Two simple pendulums *A *and *B *have length 1·0m and 4·0 m respectively at a certain place. Which pendulum will make more oscillations in 1 minute? Explain your answer.

**Solution: click this link for solution Q62**

63)A simple pendulum completes 40 oscillations in one minute. Find its (a) frequency, (b) time period.

**Solution: click this link for solution Q6**3

64) The time period of a simple pendulum is 2 s. What is its frequency? What name is given to such a pendulum ?

**Solution: click this link for solution Q6**4

## more pendulum -numericals

65) A seconds’ pendulum is taken to a place where the acceleration due to gravity falls to one-fourth. How is the time period of the pendulum affected, if at all ? Give reason. What will be its new time period?

**Solution: click this link for solution Q6**5

66) Find the length of a seconds’ pendulum at a place where *g *= 10 m/s^{2} (Take ∏= 3·14).

**Solution: click this link for solution Q6**6

##### numericals on motion for class 9 with solution

67) A pendulum completes 2 oscillations in 5 s. (a) What is its time period? (b) If *g *= 9·8 m /S^2, find its length.

**Solution: click this link for solution Q6**7

68) Compare the time periods of two pendulums of length 1 m and 9 m

**Solution: click this link for solution Q6**8

69) The time periods of two simple pendulums at a place are in ratio 2 : 1. What will be the ratio of their length ?

**Solution: click this link for solution Q6**9

70) It takes 0·2 s for a pendulum bob to move from mean position to one end. What is the time period of pendulum?

**Solution: click this link for solution Q70**

71) How much time does the bob of a seconds’ pendulum take to move from one extreme of its oscillation to the other extreme?

**Solution: click this link for solution Q**71

## relative density class 9

72) The relative density of silver is 10·5. What is the Density of silver in S.I. unit? What assumption do you make in your calculations?

73) A solid weighs 50 gf in air and 44 gf when completely immersed in water. Calculate The upthrust, The volume of the solid, and the relative density of the solid.

74) A solid weighs 30 gf in air and 26 gf when completely immersed in a liquid of relative density 0·8. Find : (i) the volume of solid, and (ii)the relative density of solid.

75) A body of volume 100 cm^3 weighs 1 kgf in air. Find : (i) its weight in water and (ii) its relative density.

76) A body of mass 70 kg, when completely immersed in water, displaces 20,000 cc of water. Find :(i) the weight of the body in water and (ii) the relative density of the material of the body.

77) A solid weighs 120 gf in air and 105 gf when it is completely immersed in water. Calculate the relative density of solid.

##### physics numericals for class 9 motion with answers

78) A car moves 100m due east and then 25 m due west. (a) What is the distance covered by the car? (b) Whatis its displacement?

79) A person walks along the sides of a square field. Each side is 100 m long. What is the maximum magnitude of displacement of the person at any time interval?

80) In the hare-tortoise race, the hare ran for 2 min at a speed of 7.5 km/h, slept for 56 min and again ran for 2 min at a speed of 7.5 km/h. Find the average speed of the hare in the race.

81) A bus takes 8 hours to cover a distance of 320 km.What is the average speed of the bus?

##### numericals on motion for class 9 with solution

82) The maximum speed of a train is 80 km/h. It takes 10 hours to cover a distance of 400 km. Find the ratio of its maximum speed to its average speed.

83) An object moves through 10m in 2 minutes and the next 10 m in 3 minutes. Calculate its average speed.

84) A car moves through 20 km at a speed of 40 km/h, and the next 20 km at a speed of 60 km/h. Calculate its average speed.

##### numericals on equation of motion for class 9

85) A boy leaves his house at 9.30 a.m. for his school. The school is 2 km away and classes start at 10.00 a.m. If he walks at a speed of 3 km/h for the first kilometer, at what speed should he walk the second kilometer to reach just in time?

## problems on mirrors and images

86) How many images will be formed if two mirrors are fitted on the adjacent walls and one mirror is fitted on the ceiling?

87) If the magnification of a body of size 1 m is 2. What is the size of the image?

88) A convex mirror used for rearview on an automobile has radius of curvature of 3 m. If a bus is located at 5 m from this mirror. Find the position, nature, and magnification of the image.

89) A candle flame is held 3 cm away from a concave mirror of radius of curvature 24 cm. Where is the image formed? What is the nature of the image?

90) An object is held 6 cm from a concave mirror of focal length 12 cm. Find the position, nature and magnification of the image.

91) An object 5 cm tall was placed in front of a spherical mirror at 20 cm distance from the mirror. If a virtual image of 10 cm tall was formed behind the mirror, find the focal length of the mirror and the position of the image. Name the type of mirror used.

92) A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located?

##### problems on mirrors and images

93) When an object is placed at a distance of 60 cm from a convex spherical mirror the magnification produced is ½. Where should the object be placed to get a magnification of 1/3?

**94) **When an object of height 1cm is kept at a distance 4 cm from a concave mirror, its erect image of height 1.5 cm is formed at a distance 6 cm behind the mirror. Find the focal length of the mirror.

**95) **An object is placed at 4 cm distance in front of a concave mirror of radius of curvature 24 cm. Find the position of image. Is the image magnified?

**96) **At what distance in front of a concave mirror of focal length 10 cm, an object be placed, so that its virtual image of size five times that of the object is obtained?

##### numericals on mirrors and images – for class 9

**97) **A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. What is the focal length of this mirror?

**98) **An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image.

99) An object 5.0 cm in length is placed at a distance of 20 cm in front of a convex mirror of radius of curvature 30 cm. Find the position of the image, its nature, and size.

**100)**An object 1 cm high produce a real image 1.5 cm high when placed at a distance of 15 cm from a concave mirror. Calculate the position of the ·image and the magnification.

**101) A bird is sitting 80 cm in front of a plane mirror ****M. ****If the mirror is now moved 0.20 m away from the bird, how does the image of the bird shift from its previous image?**

****** ********************** *********

**And here is the solution and links – for SET 1**

**Solutions- ****Physics ****problems for class 9**

(CBSE/ICSE/state/etc) set 1

(CBSE/ICSE/state/etc) set 1

**solutions** for set 1 – physics

**solutions**

1) **Force of 1000 Newton is applied on a 25 kg mass for 5 seconds. What would be its velocity?**

**Solution:**

F =1000 N

m=25kg

t= 5 sec

u=0

v=?

Acceleration = a = F/m = 1000/25 = 40 m/s^{2 }

v = u + at =0 + 40X5 = 200 m/s

**Physics problems class 9 – solutions: ** physics problems solved

**Physics problems class 9 – solutions:**

2) **A force is applied on a mass of 16 kg for 3 seconds. As the force is removed the mass moves 81 meter in 3 seconds. What was the value of the force applied?**

**Solution:**

first 3 secs (Force is present) –> next 3 secs (F is not there, so uniform velocity)

In the next 3 seconds, the mass travels with uniform velocity (as there is no force that means no acceleration).

So the velocity in the next 3 secs:

V = 81/3 = 27 m/s

This velocity was attained in the first 3 seconds when the force was present.

So in the first 3 seconds, velocity changes from 0 to 27m/s.

Therefore the acceleration in first 3 seconds caused by the force present = (27-0)/3 = 9 m/s².

So the force applied on the mass for first 3 secs= mass x acc = 16 x 9 = 144 N

**Physics problems class 9 – solutions: continued**

**Physics problems class 9 – solutions: continued**

3) **A mass of 50 kg was moving with a velocity 400 m/s. A force of 40000 N is applied on the mass and its velocity is reduced to 50 m/s after some time. What is the distance travelled by the mass during this period?**

**Solution:**

Mass = 50 kg

u = 400 m/s

v= 50 m/s

F = 40000 N

t = unknown

Distance travelled in time t =?

Acceleration = a = F/m = 40000/50 = 800 m/s^{2 }

Again, acceleration a = change of velocity /t

or, **t = change of velocity/a** = 350/800 sec

**Distance travelled: s = ut – (1/2)a t ^{2 }**

= 400 * (350/800) – (1/2) 800. (350/800)^{2 }

= 175 – 76.5 = 98.5 m

**Physics solutions: continued**

**Physics solutions: continued**

4) **A ball of 150 g mass moves with 12 m/s and bounces back after hitting a wall with 20 m/s after a small duration of 0.01 second. What was the force applied on the ball when it hits the wall?**

**Solution:**

* Physics problems for class 9 with solutions* – physics problems solved

Mass = 150 gram = 150/1000 kg = 0.15 kg

Change of velocity = 20 – (-12) = 32 m/s

T = 0.01 sec

Acceleration = change in velocity / time = 32/0.01 = 3200 m/s^{2 }

Force = mass X acc = 0.15 X 3200 N= 480 N.

**solutions: continued**

**solutions: continued**

5) **Momentum of an object changes from 100 kgm/s to 200 kgm/s in 2 seconds. What is the force applied on it?**

Solution:**Note:**Force = ma = m(v-u)/t = (mv – mu)/t = change of momentum /time = rate of change of momentum

Force= change of momentum /time = (200-100)/2 = 100/2 = 50 N

physics numerical – **Physics with solutions**

6)** A force of 200 N is applied on a body and its velocity changes from 5m/s to 10m/s in a second. What is the mass of the body?**

Solution:

mass = force/acceleration

here acceleration =a = (10-5)/1 = 5 m/s^{2}so, mass = 200/5 kg = 40 kg

**solutions: continued**

**solutions: continued**

7) **A mass of 1 kg is moving from east to west with a velocity 10 m/s. A force is applied on it for 2 seconds and its velocity becomes 5 m/s. What is the value and direction of the force?**

Solution:

Mass = 1kg

velocity = 10 m/s (east to west)

Because of the force the velocity reduces to 5 m/s in 2 secs.

acceleration = change of vel/time=5/2 = 2.5 m/s^{2 }

**Force **= mass X acceleration= 1 X 2.5 = 2.5 N.

As the velocity reduces because of force, (negative acc i.e. retardation) hence the direction of the force would be opposite to the initial direction. So the direction of the force will be west to east.

**solutions: continued**

**solutions: continued**

8)** If the distance between 2 objects is doubled then how will the gravitational force between them change?**

Solution:

F1 = GMm/r^{2}F2 = GMm/(2r)^{2}= GMm/4r^{2}so F2/F1 = ¼ ,

so the final gravitational force will be ¼ th of the initial gravitational force

**solutions: continued**

**solutions: continued**

**9) If the distance between 2 objects is halved then how will the gravitational force between them change?**

Solution:

F1 = GMm/r^{2}F2 = GMm/(r/2)^{2}=4 GMm/r^{2}

so F2/F1 = 4/1

so the final gravitational force will be 4 times of the initial gravitational force

**10) If the masses of the 2 objects are doubled then how will the gravitational force between them change?**

Solution:

F1 = GMm/r^{2}F2 = (G2M2m)/(r)^{2}=4 GMm/r^{2}so F2/F1 = 4/1

so the final gravitational force will be 4 times of the initial gravitational force

**solutions: for Q11 to Q71 – solution links are just beside the question above. Click that link to reach the page with a solution.**

**solutions: for Q11 to Q71 – solution links are just beside the question above. Click that link to reach the page with a solution.**

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