Question

A 1.9 kg book is lying on a 0.70 m -high table. You pick it up and place it on a bookshelf 2.2 mm above the floor.

During this process, how much work does gravity do on the book?

During this process, how much work does your hand do on the book?

Answer 1

(1) mass of book M = 1.9 kg;

vertical displacement of book d = 2.2 - 0.7 = 1.5 m;

(A) force due to gravity acting downward, F = mg;

F = 1.9 x 9.81 = 18.639 N;

since gravity force is acting downward and displacement of book is in upward direction, therefore angle between force F and displacement d is 180 degrees, thus workdone by gravity is;

(B) Applied force F' by the hand is equal to the force of gravity but in opposite direction; Now angle between the force F' and displacement d is zero degree.