A crate of mass M starts from rest at the top of a frictionless ramp inclined at an angle a above the horizontal. Find its speed at the bottom of the ramp, a distance d from where it started. Do this in two ways:
(a) Take the level at which the potential energy is zero to be at the bottom of the ramp with y positive upward.
(b) Take the zero level for potential energy to be at the top of the ramp with y positive upward.
(c) Why did the normal force not enter into your solution?