You drop a 2.50 kg textbook to a friend who stands on the ground 10.0 m below th

Question

You drop a 2.50 kg textbook to a friend who stands on the ground 10.0 m below the textbook with outstretched hands 1.5 m above the ground (see the figure). How much work is done on the textbook by its weight as it drops to your friend's hands? What is the change in the gravitational potential energy of the textbook-Earth system during the drop? If the gravitational Potential energy of that system is taken to be zero at ground level, what is its potential energy when the textbook is released? If the gravitational Potential energy of that system is taken to be zero at ground level, what is its potential energy when the textbook reaches the hands?

Explanation / Answer

Workdone on the textbook by its weight as it drops to your friends hand

Wg=250*9.8(10-1.5)

   =20825 J

The change in gravitational potencial energy of the textbook earth system during the drop

Wg=250*9.8(10-1.5)

   =20825 J

Potencial energy when the text book is released

Ui=250*9.8*10

=24500 J

Potencial energy when the text book reaches the hands

Ui-Wg=3675 J.

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