Question

3. A block on an incline is pushed by a hand. The hand exerts a force on the block parallel to the incline. State whether the specified quantities are positive, negative, or zero. Explain in each case.

a. The block moves up the incline and speeds up.The work done by the hand on the block. The work done by the block on the hand.

b. The block moves down the incline and speeds up (even though the hand is still pushing up along the incline.) The work done by the hand on the block. The work done by the block on the hand.

c. The block moves down the incline and slows down. (Note that the hand is now pushing down the ramp, and the ramp has friction.) The work done by the hand on the block. The work done by the block on the hand.

Answer 1

The block moves up the incline and speeds up.The work done by the hand on the block. is positive be cause the force is acting on the block it is sppeding up .The work done by the block on the hand is negative because it is moving against the gravitational force , the gravitational force component is acting on the hand so its is negative here moving up against to the gravitational force.

2 The block moves down the incline and speeds up The work done by the hand on the block is negative now

and the work done by the block on hand is is positive

3 The block moves down the incline and slows down. (Note that the hand is now pushing down the ramp, and the ramp has friction.) The work done by the hand on the block is positive because the displacement is in the direction of the force applied by hand.

The work done by the block on the hand. is negative here friction force arises which reduces the force by hand on the block