Question

multiple choice question
two cars drive down a hill. one applies its brakes and moves at a constant speed, the other doesnt and increases in speed all the way down. both cars experience forces; why does only one accelerate?
one of the cars must experience less friction with the ground.
only the car that doesnt brake experiences gravity.
only one car experiences an unbalanced (net) force.
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Explanation:

According to Newton's second law, an object accelerates when there is an unbalanced (net) force acting on it. The car that applies brakes has balanced forces (braking force counter - acts the component of gravitational force causing motion), while the non - braking car has an unbalanced force (component of gravitational force acting down the hill), causing it to accelerate. Both cars experience gravity and friction is not the main factor here.

Answer:

Only one car experiences an unbalanced (net) force.