Answer:
a. Gravity and c. Spring
Explanation:
Formula for work energy
whereas F is the force acting on the block, S is the distance traveled, and is the angle between 2 vectors F and S.
If F is perpendicular to S, then
a. Normal force is the reaction force acting from the ramp back on the wooden block. This force is perpendicular to the direction of sliding. Therefore this force would do no work.
b. Gravity is the force acting downward, this would have an angle of degrees so the work is non-zero.
c. Spring force would have the same direction as sliding so the work is non-zero.
d. Friction force would have the same direction as sliding. However, as this is a frictionless ramp, the friction coefficient would be 0. Friction force would also be zero and so as its work.