A physics textbook is launched up a rough incline with a kinetic energy of $X$ joules. When the book comes momentarily to rest near the top of the incline, it has only gained ($X-20$) joules of gravitational potential energy. About how much kinetic energy will it have when it returns to the launch point? (Hint: Remember friction and conservation of energy).
Attempt: So when the textbook goes up and reaches the point where it is at rest its GPE is $X$ joules. When it goes down and reaches the starting point its kinetic energy should by $X$ joules, I guess. Thats what I am not sure about. Does the friction act with the same force when the textbook goes down?