Question

A large crate filled with physics laboratory equipment must be moved up an incline onto a truck.

(1) The crate is at rest on the incline. What can be concluded about the force of friction acting on the crate?

A. the frictional force points up the incline

B. the frictional force points down the incline

C. the frictional force is zero

(2) A physicist attempts to push the crate up the incline. The physicist senses that if he applies slightly more force the crate will move up the incline but cannot muster enough strength to get the motion started. What can be concluded about the force of friction acting on the crate?

A. the frictional force points up the incline

B. the frictional force points down the incline

C. the frictional force is zero

(3) The first physicist gets a second physicist to help. They both push on the crate, parallel to the surface of the incline, and it moves at constant speed up the incline. How does the force exerted by the two physicists on the crate compare with the force of friction on the crate?

A. force of 2 physicists < force of friction

B. force of 2 physicists = force of friction

C. force of 2 physicists > force of friction