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Question
Certain force acting on a 20 kg mass changes its velocity from 5 m s-1 to 2 m s-1. Calculate the work done by the force.
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Solution
Mass of the object, m = 20 kg
Total work done by the force = Change in the object's kinetic energy
= `1/2 mv^2 - 1/2 m u^2`
= `1/2 m (v^2 - u^2)`
u = 5ms−1, u = 2ms−1, m = 20 kg
= 4 × 5
= 20
Hence, work done = `1/2m (v^2 - u^2)`
= `1/2 xx 20 [(2)^2 - (5)^2]`
= 10 × (−21)
= −210 J
The force will do work equivalent to 210 J. Here, the direction of force is opposite the direction of motion.
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