Abullet is dropped into a river from a very high bridge. at the same time, another bullet is fired from a gun straight down towards the water. if air resistance is negligible, how do the accelerations of the bullets compare just before they strike the water?

Explanation:

As a ball dropped into a river, its initial velocity is zero and then it is moving under the acceleration due to gravity. That means the acceleration on the ball is in vertically downwards direction which is equal to the acceleration due to gravity that means - 9.8 m/s^2.

When a bullet is fired from a gun straight downwards direction, the acceleration on the bullet is again acceleration due to gravity and it is acting acting downwards. In this case the initial velocity os not zero but acceleration is - 9.8 m/s^2.