Explanation
Answer: 2Fh
When W moves a distance h above and string at free end will move 2h below along the direction of force.
Work done=F*2h=2Fh
Question:12
A body of mass 20 kg is initially at a height of 3 m above the ground. It is lifted to a height of 2
m from that position. Its increase in potential energy is:
120 J
90 J
392 J
None of these
Explanation
Answer:392 J
Given,Mass, m = 20kg
Height m, H = 3m
Potential Energy, (PE1) = mgH ,PE1 = 20 x 9.8 x 3 PE1 = 588 joules
Now Height (h) is (3m + 2m)=5m
(PE2) = mgh
(PE2) = 20 x 9.8 x 5 (PE2) = 980 Joules
Increase in Potential Energy = PE2 - PE1 = 980 - 588 = 392 Joules