Would someone please check my physics work?

Question

I am not sure if i did these right so I'd like someone to double check them before I hand them in...thanks SOO much!

1. A person standing on a bridge at a height of 115m above a river drops a .25kg rock.
-What is the rocks mechanical energy at the time of release..relative to the rivers surface? (I got 282 J)
-What is the rocks kinetic energy after it has fallen 75 m? (98.3 J)...What is the rocks potential energy after 75 m (184J)
6. A .300 kg ball is thrown vertically upward with an inital speed of 10 m/s. If the inital potential energy is called zero, find the balls kinetic, ponetial and mechanical energies at its inital position.
For kinetic i got 15J, for potential its zero and mechanical i got 15 J.
-Now for the balls kinetic, potential and mechanical energies at its maximum height
FOr knetic i said 0 J, for potential i said 15 J and for mechanical i said 15 J.
-Now find the maximum height reached by ball-
I said 5.1 meters

Answer 1

What is meant by "mechanical energy"? If that means the sum of potential and kinetic energies, then the answer is 287.5 J. Zero kinetic and all potential. Potential is F*d = m*g*d = .25 * 10 * 115.

Kinetic energy after 75m is 187.5 J.

Potential energy at that point is 100 J

For problem 6.
Kinetic = 1/2 * m * v^2 = 1/2 * .3 * (10)^2 = 15 J

Your answers at the top of the path are correct.

since potential energy = m*g*h = 15 J and m = .3 and g = 10, then h = 5 m.

Answer 2

1. You messed up on the conditions at 75 m. The way you worked it, you thought it was 75 m above the river. Problem says it has fallen 75 m from the bridge.

6.Good Work!

ppgpca worked it OK but considers g = 10