Question

1. a group of girls are riding their bikes along a path that has a small hill. the girls pedal quickly to reach the top of the hill, and then take their feet off the pedals to \coast\ the downhill part of the path. which of the following best describes the motion of the girls bikes after they reached the bottom of the hill?

a. their bikes will begin to speed up because gravity will no longer be pulling on the bikes.

b. their bikes will begin to slow down because of the friction between the wheels and the ground.

c. their bikes will begin to quickly speed up until the friction between the pedals and the ground causes them to stop.

d. their bikes will increase their speed because the friction between the pedals and the chain increases.

Explanation:

Step1: Analyze Option A

When they take feet off pedals, gravity doesn't pull on bikes anymore (as no pedaling force). But there is still friction. So bikes won't speed up.

Step2: Analyze Option B

Friction between wheels and ground causes bikes to slow down, not stop immediately.

Step3: Analyze Option C

When pedaling stops (feet off pedals), friction between pedals and ground doesn't increase. Friction between wheels and ground is main factor.

Step4: Analyze Option D

After reaching bottom (no pedaling), friction between wheels and ground acts against motion. So bikes slow down.

Answer:

D. Their bikes will begin to slow down because of the friction between the wheels and the ground.