A crate sits in the middle of the bed on a flatbed truck that is traveling at 80 km/h on a straight, level road. The coefficient of static friction between the crate and the truck bed is 0.40. When the truck comes uniformly to a stop, the crate does not slide, but remains stationary on the truck. What is the minimum stopping distance for the truck so the crate does not slide on the truck bed? THINKING IT THROUGH. There are three forces on the crate, as shown in the free-body diagram in ▼ Figure 4.23 (assuming that the truck is initially traveling in the +x-direction). But wait. There is a net force in the −x-direction, and hence there should be an acceleration in that direction. What does this mean? It means

that relative to the ground, the crate is decelerating at the same rate as the truck, which is necessary for the crate not to slide – the crate and the truck slow down uniformly together.

The force creating this acceleration for the crate is the static force of friction. The acceleration is found using Newton’s second law, and then is used in one of the kinematic equations to find the distance.

Transcribed Image Text:

N A FIGURE 4.23 Free-body diagram See Example 4.12 for description.