A rock is thrown vertically upward at an initial velocity of 70 m/s. What is the approximate acceleration of the rock when it reaches its maximum height (assume upward is the positive y direction)?

Zero.

Explanation:

Given that a rock is thrown vertically upward at an initial velocity of 70 m/s. What is the approximate acceleration of the rock when it reaches its maximum height

(assume upward is the positive y direction)?

Since the reached the maximum height, the final velocity V will be equal to zero.

Using the first equation of motion to find the time.

And since it is a vertical direction, and not horizontal, the acceleration a will be equal to zero.

the answer is to check all of them! they all apply well at least i think so!