A mass m slides down a smooth inclined plane from an initial vertical height h, making an angle a with the horizontal. (a) The work done by a force is the sum of the work done by the components of the force. Consider the components of gravity parallel and perpendicular to the surface of the plane. Calculate the work done on the mass by each of the correspondents, and use these results to show that the work done by gravity is exactly the same as if the mass had fallen straight down through the air from a height h.
(b) Use the work-energy theorem to prove that the speed of the mass at the bottom of the incline is the same as if it had been dropped from height h, independent of the angle a of the incline. Explain how this speed can be independent of the slope angle.
(c) Use the results of part (b) to find the speed of a rock that slides down an icy frictionless bill, staining from rest 15.0 m above the bottom.