19. You lift a heavily packed carton of mass ‘m’ in vertically upward direction through a height h. What is the work done (a) by you on the carton, (b) by force of gravity on the carton?
Answers
answer : (a) mgh (b) -mgh
I lift a heavily packed cartoon of mass m in vertically upward direction through a height h.
Total workdone by me on the cartoon is zero because net displacement covered by cartoon is zero.
(a) so, workdone by me on the cartoon = force applied by me on cartoon × displacement covered by cartoon due to applied force.
= mg(upward) .h (upward)
= mghcos0°
= mgh ( positive)
(b) workdone by force of gravity on the cartoon = gravitational force acting on the cartoon × displacement of cartoon
= mg (downward) . h (upward)
= mghcos180°
= -mgh (negative)
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Answer:
mgh (+ve wrk)
-mgh (-ve wrk)