Question
An astronaut shipwrecked on a remote planet with unidentified characteristics is on top of a cliff, which she wishes to descend. She does not know acceleration due to gravity on the planet, and she has only a good watch with which to make measurements. She wants to find out the height of cliff, and to do this she makes two measurements. Initial, she lets the rock fall from rest off the cliff edge; she finds that the rock takes 4.15 s to reach the distant ground below the cliff. Second, she releases rock from the similar spot but tosses it upward so that it rises 2 m before falling to the distant ground below the cliff. This time the rock takes 6.30 s to reach the ground. What is height of the cliff?