Final answer:
Option (B), Friction is a force that typically opposes motion and causes objects to slow down, yet it can also cause objects to speed up, such as a package on a moving conveyer belt where friction helps the package to accelerate.
Step-by-step explanation:
Friction is a force that opposes relative motion between surfaces in contact. However, it can also cause an object to speed up in certain situations, like when you walk forward; friction between your feet and the ground provides the necessary grip for you to push off and propel yourself forward. The answer to the student's question about a scenario where friction causes an object to speed up is: a package on a moving conveyor belt. Here, the frictional force between the package and the belt causes the package to accelerate to the same speed as the belt.
Regarding the options provided:
- A sled on snow - experiences friction, which generally slows it down.
- A package on a moving conveyer belt - friction between the belt and package causes the package to accelerate.
- Air resistance on a moving car - this form of friction, also known as drag, typically acts to slow the car down.
- Sliding a book across your desk - friction opposes the motion, resulting in the book slowing down.
Friction is therefore identified as a resistive force that opposes motion but can also facilitate motion under the right circumstances. When it comes to walking or the motion of the package on the conveyor belt, friction is essential for acceleration and movement.