Question

A force applied on a body of mass 4kg for 5 second changes its velocity from 10m/s to 20m/s

Answer 1

Power = workdone / time

= (Force × displacement)/ time

= (mass × acceleration × displacement) × time

initial velocity = 10m/s

final velocity = 20m/s

time taken = 5s

using 1st eq. if motion

acceleration = (final velocity- initial velocity)/ time

= (20-10)/5

= 10/5

= 2m/s^2

using third eq. of motion

2as = v^2 -u^2

2(2)(s) = (20)^2 -(10)^2

s = 300/4

s = 75

by substituting these values

power = (4 × 3 × 75)/5

= 180watt.

Answer 2

Power = Work done / Time

Work done is also defined as the change in KE of an object.

As change in KE is 1/2M(Vf^2-Vi^2)

here vf is final velocity

vi is initial velocity.

Change in KE will be 1/2 4 ( 20square-10square)

Time is 5s.

Substitute values to calculate power.

Hope you get your answer.