Class 8 Physics – Energy Numericals (Step-by-Step Solutions)

Title: Class: 8 Physics – Energy (Numerical Problems – Full Set)

Question 1:

A force of 30 N acts on a body and moves it through a distance of 5 m in the direction of
force. Calculate the work done.

Solution:

Given:
Force F = 30 N
Distance d = 5 m
Work done = ?

Formula:
W=F×d

Substitution:
W = 30 N × 5 m
W = 150 N m
We know:
1Nm=1J

Final Answer:
W = 150 J

Question: 2

A man lifts a mass of 20 kg to a height of 2.5 m. Assuming that the force of gravity on 1
kg mass is 10 N, find the work done by the man.

Solution :
Given:
Mass m = 20 kg
Height h = 2.5 m
Force on 1 kg = 10 N
Work done = ?

Step 1: Find Force
Force on 1 kg = 10 N

, Force on 20 kg = 20 × 10 N
Force F = 200 N

Step 2: Formula
W=F×d

Step 3: Substitution
W = 200 N × 2.5 m
W = 500 N m

We know:
1Nm=1J

Final Answer:
W = 500 J


Question: 3
A body when acted upon by a force of 10 kgf moves through a distance of 0.5 m in the
direction of force. Find the work done by the force. Take 1 kgf = 10 N.

Solution:

Given:
Force = 10 kgf
Distance d = 0.5 m
1 kgf = 10 N
Work done = ?

Step 1: Convert Force into Newton
1 kgf = 10 N
10 kgf = 10 × 10 N
Force F = 100 N

Step 2: Formula
W=F×d

Step 3: Substitution
W = 100 N × 0.5 m
W = 50 N m