IIT JEE , AIEEE Forum - Physics , Mechanics

Ank999

The work done by the external forces on a system equals the change in

a) total energy

b) kinetic energy

c) potential energy

d) none of these

Plz explain the ans

ans is (a)

krishna.gopal

Suppose you pull up a mass of 1 kg by a force of 20 N to a height of 20 meter.
Work done by you=20*20=400J

Net acceleration of body=(F-mg)/m=(20-1*10)/1=10m/s^2
Final velocity = sqrt(2*10*20)=20m/s
So increase in KE of body =200J
increase in PE of body = mgh=1*10*20=200J
Work done=change in KE+change in PE=change in total energy

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