When a mass on a spring is at maximum displacement, what quantity is at a minimum?
a. acceleration
b. velocity
c. net force
d. amplitude

b. velocity

Explanation:

The spring is at maximum displacement when it experiences maximum net force and so the maximum acceleration. (F = - k x = ma ).

The displacement of the spring determines the amplitude. Hence, maximum displacement means maximum amplitude.

At the maximum displacement, the potential energy (P.E. = 0.5 k x²) possessed by the spring would be maximum and minimum kinetic energy (K.E.= 0.5 m v²). This means that the spring would have minimum velocity at maximum displacement.

grav forces affect all objects magnetic forces affect magnetic objects and electric currents

the displacement produced by the body.  

the amount of force subjected to the body.  

the angle between the direction of force and displacement