1) Is it possible for the frictional force to increase the mechanical energy of a system?

2) How a car's airbag works in terms of momentum? AND in terms of energy?

3) A solid sphere, hoop, and disk (all with same mass and radius) are rolled up an incline with (potentially) different initial speeds. They each reach the same height up the incline. Compare the initial speed that they each enter the incline and explain the order. Why is one greater than another and/or why are they the same?

4) A ball rolls up a ramp which abruptly ends with the ramp dropping straight down. The ball launches off the end of the ramp while still traveling at an upward trajectory, goes through projectile motion, and returns to the same height as the base of the ramp. Ignoring any slowing friction (rolling friction), when the ball returns to the height of the ramp's base, the ball lands with a greater speed than when it entered the ramp.