Question

49. A car is parked on a hill. In order to keep the car from rolling downhill, how great must the static friction acting on the car be?

a.
equal to the force pulling the car downhill
b.
greater than the force pulling the car downhill
c.
greater than the force pulling the car uphill
d.
smaller than the force pulling the car uphill

Answer 1

The answer is (a.) equal to the force pulling the car downhill

As long as the static friction of the car is least equal to the force that pulls the car downhill, the car is a rest. The static frictional force of the car increase to prevent any relative motion.