Question
A child is moving on a skateboard at the speed of 2 ms−1. After a force acts on him, his speed becomes 3 ms−1. Find the work done by the external force on the child, given the mass of the child is 20 kg.
Answer: Option B
:
B
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B
Let initial velocity of the child be v1 and final velocity be v2
Given, v1=2 ms−1, v2=3 ms−1 and mass of the child =20 kg.
Since the child is in motion, he will have a kinetic energy of mv22, which will be increased after an application of force by an external agent on him.
Now, Applying work energy theorem ,
Work done by the external force on the child =mv222–mv212
=20×(9–4)2
=10×5=50 J
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