# 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/s^{2}]

That means, mg = 9.8

=> mass m = 9.8/g = 9.8/9.8 = 1 kgSo, 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/s^{2}[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/s^{2}= 1 m/s^{2}

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/s^{2}= 10 m/s^{2}

Force applied F = 100 N

mass m = ?

we know, F = ma

=> m =F/aSo, here, mass m = 100/10 kg = 10 kg [Answer]