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.
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