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OBINPHYS8 2.CQ.003.

A book is accidentally left on the roof of a car as the driver drives away. As the car and the book move with constant velocity along

the street, what must be true about the magnitude (size) of the forces acting on the book? Choose the best answer.

There is no force of gravity acting on the book because the book rests on the car and does not fall.

Static friction between the book and the roof of the car has the same magnitude as kinetic friction caused by air

resistance.

O Kinetic friction acting on the book due to air resistance is larger than static friction between the roof of the car and the

book.

Static friction between the book and the car is larger than air friction in the other direction, and this allows the book to

move forward.

Correct. Since the book is not accelerating, the net force acting on the book must be zero. The forces are balanced.