Question

A rock is thrown straight up. At the top of the trajectory, the velocity is momentarily zero. Does this imply that the force acting on the object is zero? Explain your answer.

a) Yes, because there is no motion
b) No, because gravity still acts on the rock
c) Yes, because velocity is zero
d) No, because velocity is not related to force

Answer 1

The fact that the velocity of a rock thrown straight up is momentarily zero at the top of its trajectory does not imply that the force acting on the object is zero. Gravity still acts on the rock, causing it to decelerate and then accelerate downward.

Step-by-step explanation:

The fact that the velocity of a rock thrown straight up is momentarily zero at the top of its trajectory does not imply that the force acting on the object is zero. The correct answer is b) No, because gravity still acts on the rock.

Even though the velocity is momentarily zero, the force of gravity is still acting on the rock and causing it to decelerate until it reaches its highest point. Once at the top, the force of gravity reverses the direction of the rock, causing it to accelerate downward.

Therefore, the force acting on the object is not zero because gravity is still present and exerting a force on the rock.