College Physics with MasteringPhysics 7th Edition by Jerry Wilson,Anthony Buffa,Bo Lou

Exercise 123

A crate sits in the middle of the bed of a flatbed truck. The driver accelerates the truck gradually from rest to a normal speed, but then has to make a sudden stop to avoid hitting a car. If the crate slides as the truck stops, the frictional force would be (a) in the forward direction, (b) in the backward direction, (c) zero.