An object is thrown vertically upwards. At its maximum height, which of the following quantity becomes zero?

We need to determine which quantity becomes zero at the maximum height when an object is thrown vertically upwards.

At maximum height, the velocity of the object becomes zero ($$v = 0$$). Therefore, the momentum $$p = mv$$ is also zero since $$v = 0$$.

In contrast, the potential energy at maximum height is maximum ($$PE = mgh$$) and hence is not zero.

Furthermore, acceleration due to gravity $$g$$ acts throughout the motion; at maximum height $$a = g = 9.8$$ m/s$$^2$$ (downward), so it is not zero.

Similarly, the gravitational force $$F = mg$$ remains nonzero ($$F = mg \neq 0$$) at that point.

Consequently, the only quantity that becomes zero at the maximum height is the momentum, and thus the correct answer is Option A.