High School Physics

# Speed and velocity numerical for class 9

This tutorial on Speed and velocity numerical is for class 9 physics students of CBSE and ICSE boards. This also covers AS Physics Kinematics (motion).

There are three ways in which the equation for velocity v = s/t can be rearranged, depending on which quantity we want to determine.
Here, v denotes velocity, s is displacement, and t is time.

velocity v = s/t = displacement/time
displacement s = v x t = velocity x time
time t = s/v = displacement/velocity

Note also that we can, of course, use the same equations to find speed and distance.
Here, v denotes speed, s is distance, and t is time.

speed v = s/t = distance/time
distance s = v x t = speed x time
time t = s/v = distance/speed

1 ) A car is traveling at 15 m s-1. How far will it travel in 1 hour?

Solution:

v = 15 m/s
t = 1 h = 3600s
distance traveled = s = ?
Choose the appropriate version of the equation and substitute in the values; include units:
s =v t =15m/s x 3600 s = 54000 m = 54 km
The car will travel 54 km in 1 hour.

2) The Earth orbits the Sun at a distance of 150000000 km: How long does it take light from the Sun to reach the Earth? (Speed of light in space = 3 x 10^8 m/s.)

Solution:

v = 3 x 10^8 m/s
s = 150000000 km = 150000000000 m = 1.5 x 10^11 m

t = s/v= (1.5 x 10^11)/( 3 x 10^8) seconds = 500 seconds
Light takes 500 seconds to travel from the Sun to the Earth.

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