Question

your friend’s car died again and needs to be pushed off of the road. this time however, the road where it stopped is smooth, but the shoulder is muddy and full of holes and gravel. which of the following is true about the forces involved in moving the car this time? (1 point)
it requires less force to start a stopped car moving on smooth surface than to keep the car moving on the very rough surface of the shoulder.
it requires an equal amount of force to start the stopped car moving on a smooth and to keep the car moving on the very rough surface of the shoulder.
it requires more force to start a stopped car moving on smooth surface than to keep the car moving on the very rough surface of the shoulder.

Explanation:

To solve this, we analyze static and kinetic friction. Static friction (to start moving) on a smooth surface is relatively low. Kinetic friction (to keep moving) on a rough surface (shoulder) is high because rough surfaces increase friction. So starting on smooth (static friction) needs less force than keeping moving on rough (kinetic friction on rough).

Answer:

It requires less force to start a stopped car moving on smooth surface than to keep the car moving on the very rough surface of the shoulder.