28) This question asks us to find the speed of the ball relative to the rock when the ball has fallen 28 meters further than the rock.
The ball is thrown down with a speed of 36 m/s at a time 2.1 s after the rock is dropped.
At t = 2.1 seconds, when the ball is thrown, the rock is 22.05 meters below the ball. This tells us that the ball will be 28 meters lower than the rock at some time after t = 2.1 seconds.
Here is the trick to this problem: after the first 2.1 seconds, both the ball and the rock are influenced by the same acceleration. This means that both the ball and the rock will have the same change in velocity at any time after 2.1 seconds. The ball and the rock will have the same relative speed at any point after t = 2.1 seconds.
Answer: A
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