Question

consider a truck that is driving around town carrying a package, as shown below. assuming that there is sufficient friction to prevent the package from sliding around inside or the truck, in which direction (if any) must the force of friction push the block when: 1. the truck is speeding up? 2. the truck is slowing down? (you do not need a separate written work submission for this question but instead can just type in your explanation here.)

Explanation:

Step1: Analyze when truck is speeding up

When the truck is speeding up, the package has a tendency to stay behind due to inertia. So the friction force must act in the forward - direction to make the package move with the accelerating truck.

Step2: Analyze when truck is slowing down

When the truck is slowing down, the package has a tendency to move forward due to inertia. So the friction force must act in the backward - direction to slow down the package along with the truck.

Answer:

1. When the truck is speeding up, the force of friction pushes the block in the forward direction.
2. When the truck is slowing down, the force of friction pushes the block in the backward direction.