Consider a rock with mass m dropped from rest off a cliff of height h.
1. If we want to apply conservation of energy to the falling rock, what do we need to include in our system?
2. Let us set the gravitational potential energy V=0 when the rock is at the bottom of the cliff. With this convention, what is the gravitational potential energy and the kinetic energy of the system when the rock is at the top of the cliff?
3. What is the gravitational potential energy and kinetic energy of the system just before the rock hits the ground at the bottom of the cliff?
4. Using your answers to parts 2 and 3 as the end points, make a rough sketch of gravitational potential energy and kinetic energy vs. time during the entire period of the rock's motion from top to bottom of the cliff.
KE = 1/2 m v^2
PE = mgz
The Attempt at a Solution
1. earth, rock, and cliff?
2. PE = m * 9.8 m/s^2 * h; KE = 0?
3. PE = m * 9.8 m/s^2 * h? KE = (1/2)m(h/t)^2?
4. Is this like an x-y graph, where x is time and y is energy? if so, then gravitational energy would be like a straight line from top to 0, and KE would be like from the origin to the top right, so like two straight lines criss-crossing; an X