Question

find the work done to change the velocity of a thousand kg cars from 10 M per second to
5 m per second in 4 second

Answer 1

work done is equal to 400 joules and kinetic energy before is 50 kilojoules and after is 12.5 kilojoules.
We know that,
work done = power x time
=> work done = 100 x 4 = 400 joules
kinetic energy = mv²/2
Hence kinetic energy before power application,
E₁ = 1000  x 10²/2
= 1000x 50
= 50 kilojoule
Kinetic energy after applying power,
E₂ = 1000 x 5²/2
= 500 x 25
=12500
= 12.5 kilojoules