relative motion

Question

A rock climber stands on top of a 60 m -high cliff overhanging a pool of water. He throws two stones vertically downward 1.0 s apart and observes that they cause a single splash. The initial speed of the first stone was 2.3 m/s .

How long after the release of the first stone does the second stone hit the water?

What was the initial speed of the second stone?

What is the speed of the first stone as it hits the water? What is the speed of the second stone as it hits the water?

Answer 1

Hey Katherine,

1. This first question is the same as asking how long it takes the first stone to hit the water.
2. You can use d = v_it + 1/2at² with the first stone to determine the time it took to reach the water. Looks like this will involve a quadratic equation. Just make sure that your d, v_i, and a are all negative in your set-up.
3. For the second question, subtract one second from that time and use the same equation to solve for v_i.
4. Use v_f = v_i + at to find the final speeds of each stone.