A mass attached to the end of a spring is pulled out and released on a surface with friction.The work
Done on the mass by the force exerted by the spring
A)never has the same sign as the change in energy owing to friction.
B)always has the same sign as the change in energy owing to friction.
C)has the same sign as the change in energy owing to friction during one half of each cycle.
D)never has the same sign as the change in energy owing to friction if the force of friction is greater than the spring force.
E)always has the same sign as the change in energy owing to friction if the force of friction is greater than the spring force.

Question

A mass attached to the end of a spring is pulled out and released on a surface with friction.The work 
Done on the mass by the force exerted by the spring
A)never has the same sign as the change in energy owing to friction. 
B)always has the same sign as the change in energy owing to friction. 
C)has the same sign as the change in energy owing to friction during one half of each cycle. 
D)never has the same sign as the change in energy owing to friction if the force of friction is greater than the spring force. 
E)always has the same sign as the change in energy owing to friction if the force of friction is greater than the spring force.

Quizplus · Accepted Answer

During one half of each cycle, the force exerted by the spring is in the opposite direction to the displacement of the mass, so the work done on the mass by the spring force is negative. During the other half of each cycle, the force exerted by the spring is in the same direction as the displacement of the mass, so the work done on the mass by the spring force is positive. The change in energy owing to friction is always negative (energy is lost to the surroundings), so during the first half of each cycle, the work done by the spring force has the same sign as the change in energy owing to friction, and during the second half of each cycle, the work done by the spring force has the opposite sign as the change in energy owing to friction. Therefore, C is the correct choice.

A Mass Attached to the End of a Spring Is