A worker applies force to a wheeled cart on a level floor. The cart moves at a constant velocity as long as the worker continues to apply force. What conclusion can be reached about friction between the cart and the floor?


A

It is zero as long as the cart is moving at a constant velocity.


B

It is positive until the cart is in motion, but is zero when the cart is in motion.


C

It is equal in magnitude to the worker’s force, but opposite in direction.


D

It is equal in magnitude to the worker’s force, and has the same direction