According to the conservation of mechanical energy, the kinetic energy just before the ball strikes the ground is equal to the potential energy just before it fell.
Therefore, we can say KE = PE
We know that PE = m·g·h
Which means KE = m·g·h
We can solve for h:
h = KE / m·g
= 20 / (0.15 · 9.8)
= 13.6m
The correct answer is: the ball has fallen from a height of 13.6m.
The Earth's radius is 6371 km. So that's our distance from the center when we're on the surface.
The Shuttle astronaut's distance from the center, when s/he's in orbit, is 330 km greater ... that's 6701 km.
The force of gravity is inversely proportional to the distance between the center of the Earth and the center of the astronaut. So, in orbit, it's
(6371/6701)^2 = 90.4 %
of its value on the surface.
Potential and kinetic energy
This is either a trick question or a very hard one. In the first case: An electric field cannot occur inside a conductor (or by using the superposition principle you find out that at this point your electric fields cancel each other out)... Or you must use the laplace equation and proper boundary conditions to solve for the electrostatic potential
<span>Edit: Considering the center of mass of the plate is on the plate</span>
