JEE Main · 2021 · 22 Jul 2021 · Shift 2 · Work, Power & Energy

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A porter lifts a heavy suitcase of mass 80 kg and at the destination lowers it down by a distance of 80 cm with a constant velocity. Calculate the work done by the porter in lowering the suitcase.
(take

g = 9.8 ms^{- 2}

)

(A)-627.2 J✓ Correct
(B)-62720.0 J
(C)+627.2 J
(D)784.0 J

Answer: (A)

Solution

The suitcase comes down

0.8

m at constant velocity, so its kinetic energy does not change and the porter's upward force balances the weight,

F = m g

. That force points opposite to the displacement, so the work done by the porter is negative:

W = - m g h = - (80) (9.8) (0.8) J

The porter does

- 627.2

J of work in lowering the suitcase.

JEE Main · 2021 · 22 Jul 2021 · Shift 2 · Single correct option

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