Imagine you throw a tennis ball vertically into the air. At the exact top of its trajectory it is at rest. What is the magnitude of its acceleration at this point?
A) $9.8 \mathrm{~m} / \mathrm{s}^{2}$
B) $-9.8 \mathrm{~m} / \mathrm{s}^{2}$
C) $0

Question

Imagine you throw a tennis ball vertically into the air. At the exact top of its trajectory it is at rest. What is the magnitude of its acceleration at this point?
A) $9.8 \mathrm{~m} / \mathrm{s}^{2}$
B) $-9.8 \mathrm{~m} / \mathrm{s}^{2}$
C) $0<|\vec{a}|<9.8 \mathrm{~m} / \mathrm{s}^{2}$
D) 0
E) Other (specify)

Quizplus · Accepted Answer

At the top of its trajectory, the velocity of the tennis ball is 0 m/s, but it is still accelerating due to gravity at $9.8 \mathrm{~m} / \mathrm{s}^{2}$ downwards. The magnitude of acceleration does not depend on the direction, hence the answer is $9.8 \mathrm{~m} / \mathrm{s}^{2}$.

Imagine You Throw a Tennis Ball Vertically into the Air 9.8 m/s29.8 \mathrm{~m} / \mathrm{s}^{2}9.8 m/s2

Imagine You Throw a Tennis Ball Vertically into the Air $9.8 \mathrm{~m} / \mathrm{s}^{2}$