question_answer

A block of 1 kg is kept on a rough surface of an elevator moving up with constant velocity of 5m/s. In 10 seconds work done by normal  reaction (the block does not slide on the inclined surface)

(i) from ground frame is 320 J

(ii) is equal to work done by friction force in elevator frame

(iii) is equal to work done by friction in ground frame of the three statements given above, the one that is true is given by the choice

A) Only (i)

B) (ii) and (iii)

C) (i) and (ii)

D) only (iii)

Correct Answer: A

Solution :

[a] W.D. from ground frame \[=6.4\times 50= 320 \,J\] From elevator frame, displacement = 0. \[\operatorname{N} cos 37{}^\circ  = 8\times 0.8 = 6.4 N\]