You drop a 2 kg book to a friend who stand on the ground at distance d=10.0 m below, if your friends out streched hand at distance d=1.50 m above the ground. (a) how does the work wg does the gravitational force do on the book as it is drop to her hands? (b) what is the change u in the gravitational potential energy of book earth system drop? if the gravitational potential energy u of that system is taken be zero by ground level

Part(a) The work done by gravitational force on the book as it is dropped to her hands is 167 Joules

Part(b) The change in the gravitational potential energy() of book earth system is -167 Joule

Explanation:

Part (a)

Since the work done (W)= Force(F)x Displacement(D) in the direction of force

Here force is applied by gravity in downward direction (towards the center of the earth),

And displacement in the direction of force is D= (10-1.5) m = 8.5 m

Therefore work done ,

where mass, m =2 kg and acceleration due to earth's gravity ,

=>

Thus the work done by gravitational force on the book as it is dropped to her hands is 167 Joules

Part (b)

By the work energy theorem , Change in the gravitational potential energy ()= - Work done by gravitational force ()

=>

Thus  the change in the gravitational potential energy() of book earth system is -167 Joule