High School Physics

# Numericals on Second Law of Motion class 9

In this post, we will solve numerical problems based on Newton’s Second Law of Motion. Basically, these problems will be solved with the help of the equation of force in terms of the mass and acceleration of a body, that comes from the second law of motion. This set of numerical questions is good for class 9 students.

Formula Used

F = m a
a = F/m
m = F/a
F = force applied, m = mass of the body, and a = acceleration of the body.

Numericals based on the Second Law of Motion for class 9

1] 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?

Solution:

Weight = 9.8 N …………. (1)
We know, weight = mg [ here, m = mass, and g = acceleration due to gravity 9.8 m/s2 ]
That means, mg = 9.8
=> mass m = 9.8/g = 9.8/9.8 = 1 kg
So, the mass of the body = 1 kg. [Answer]

Force = 20 N

Force = mass x acceleration
So, acceleration = force/mass = 20/1 m/s^2 = 20 m/s2 [Answer]

2] A body of mass 50 kg is moving with a velocity of 5 m/s. A force acts on it and its velocity changes to 10 m/s after 5 seconds. What is the value of the applied force in N?

Solution:

mass m = 50 kg

change in velocity = (10-5)m/s = 5 m/s
Time duration t = 5 s
Acceleration a = change in velocity/t = 5/5 m/s2 = 1 m/s2

Applied force F = ma = 50×1 N = 50 N

3] A body is moving with a velocity of 15 m/s. A force of 100 N acts on it and its velocity changes to 25 m/s after 1 second. What is the mass of the body?

Solution:

change in velocity = (25-15)m/s = 10 m/s
Time duration t = 1 s
Acceleration a = change in velocity/t = 10/1 m/s2 = 10 m/s2
Force applied F = 100 N
mass m = ?

we know, F = ma
=> m =F/a
So, here, mass m = 100/10 kg = 10 kg [Answer]