Please help me with this!! I am really confused about it...
1. A 75 kg. man steps off the end of a diving board, and hits the water at 7.7 m/s. Ignoring air resistance, what was the mans PE (potential energy) right before he stepped off the diving board?
*I know that the formula for potential is equal to its weight multiplied times its height. And I know that weight is mass times acceleration due to gravity, so then PE = mgh. I don't know how to use this information to find the PE since I don't know that height of the diving board...
2. How high is the diving board?
I don't know how to find the height of the diving board... since i don't the PE because if I knew the PE i could find the height by switching the original equation (PE = mgh) and make it into (h = PE/mg). I really need to know how to find the height and the potential energy in this problem!! Please explain these to me!?! Thank you!!
5 answers
Whatever Pe he had up on that board relative to the water surface is all Ke when he hits the water.
Ke = (1/2) m v^2
= (1/2) (75) (7.7)^2 Joules
THAT is the Pe he had up on the board :)
2. NOW YOU ARE ON A ROLL
Pe = m g h = answer to #1 above :)
m g h = 2223
75 * 9.81 * h = 2223
h = 3.02 meters