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Questions on Energy Transitions

Q8. A bookshelf is 1 metre above the floor. As a book falls from the shelf to the floor it loses 7.5 J of potential energy.

(a)

(i) Select the correct statement about the kinetic energy of the book.

  • An object has gravitational potential energy by virtue of its position in the gravitational field. The higher up it is, the more gravitational potential energy it has.
  • An object has kinetic energy by virtue of its movement. The faster it goes the more KE it has.
  • An objet moves faster as it falls.
A
 While the book was resting on the shelf it had 7.5 J of kinetic energy.
B
 While the book was falling, its potential energy was being transferred into kinetic energy.
C
 While the book was falling its kinetic energy remained constant.
D
 While the book was falling it lost kinetic energy.

1 mark

(ii) How much kinetic energy does the book have just before it hits the floor?

7.5 J

All of its GPE will have changed into KE just before it makes contact with the floor - it then gets changed into heat and sound energy.

1 mark

(b) When the book hits the floor it stops and loses all its kinetic energy. What happens to this energy?

It is transferred to the surroundings - into sound and heat energy.

1 mark

Maximum 3 marks