pulls on a crate of mass m that is in contact with a rough surface. The figure shows the magnitudes and directions of the forces that act on the crate in this situation. represents the weight of the crate. represents the normal force on the crate, and represents the frictional force.
-Which statement best describes the motion of the crate?
A)The crate must be at rest.
B)The crate must be moving with constant velocity.
C)The crate must be moving with constant acceleration.
D)The crate may be either at rest or moving with constant velocity.
E)The crate may be either at rest or moving with constant acceleration.

Question

pulls on a crate of mass m that is in contact with a rough surface. The figure shows the magnitudes and directions of the forces that act on the crate in this situation.  represents the weight of the crate.  represents the normal force on the crate, and  represents the frictional force. 
-Which statement best describes the motion of the crate?
A)The crate must be at rest. 
B)The crate must be moving with constant velocity. 
C)The crate must be moving with constant acceleration. 
D)The crate may be either at rest or moving with constant velocity. 
E)The crate may be either at rest or moving with constant acceleration.

Quizplus · Accepted Answer

The net force acting on the crate is zero because the weight is balanced by the normal force and the frictional force. Therefore, the crate may either be at rest (if static friction is greater than or equal to the applied force) or moving with constant velocity (if kinetic friction is less than the applied force). It cannot be moving with constant acceleration because there is no net force acting on it to cause acceleration.

Pulls on a Crate of Mass M That Is in Contact