A mass attached to the end of a spring is pulled out and released on a surface with friction.The work $\overrightarrow { \mathbf { F } } _ { sp } \cdot d~ \overrightarrow { \mathbf { x } }$ 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

Quizplus · Accepted Answer

The work done by the spring force is positive when the spring is returning to its equilibrium position and negative when moving away. Friction always dissipates energy, so its energy change is always negative. Thus, during one half of each cycle, the signs will match.

A Mass Attached to the End of a Spring Is F→sp⋅d x→\overrightarrow { \mathbf { F } } _ { sp } \cdot d~ \overrightarrow { \mathbf { x } }Fsp​⋅d x

A Mass Attached to the End of a Spring Is $\overrightarrow { \mathbf { F } } _ { sp } \cdot d~ \overrightarrow { \mathbf { x } }$