Question

1. what is an example of how friction can be helpful?

a. a skateboard ramp.
b. a seatbelt in a car.
c. the brakes on a car.
d. the wheels on a bicycle.

Explanation:

• Option a: A skateboard ramp mainly relates to motion and potential/kinetic energy conversion (gravity - related), not friction's helpful aspect.
• Option b: A seatbelt in a car is about inertia (Newton's first law) - preventing the body from continuing in motion when the car stops, not friction.
• Option c: The brakes on a car use friction. When you apply brakes, the brake pads rub against the wheels (or discs). This frictional force opposes the motion of the wheels, slowing down or stopping the car. So, it shows how friction can be helpful (in stopping the vehicle).
• Option d: The wheels on a bicycle reduce friction (rolling friction is less than sliding friction). They are designed to move smoothly, not to utilize friction as a helpful factor in the context of the question.

Answer:

C. The brakes on a car.