Answer:
At point A, the cart has high potential energy. At point b, the cart is pulled down by gravity. At point c, the cart gains its highest kinetic energy. At point d, the cart returns back to the same state but with lower potential energy.
"B" When an object moves away from us, the light is shifted to the red end of the spectrum, as its wavelengths get longer.
No additional force is required because it's already going downhill
