A 4.0-kg block is lowered down a 37° incline a distance of 5.0 m from point A to point B.A horizontal force (F = 10 N)is applied to the block between A and B as shown in the figure.The kinetic energy of the block at A is 10 J and at B it is 20 J.How much work is done on the block by the force of friction between A and B?
A)−58 J
B)−53 J
C)−68 J
D)−63 J
E)−47 J

Question

A 4.0-kg block is lowered down a 37° incline a distance of 5.0 m from point A to point B.A horizontal force (F = 10 N)is applied to the block between A and B as shown in the figure.The kinetic energy of the block at A is 10 J and at B it is 20 J.How much work is done on the block by the force of friction between A and B? 
A)−58 J 
B)−53 J 
C)−68 J 
D)−63 J 
E)−47 J

Quizplus · Accepted Answer

First, we can use the work-energy principle to find the work done on the block by the net force between A and B:

W_net = K_B - K_A 
W_net = 20 J - 10 J 
W_net = 10 J

This tells us that the net force done on the block between A and B (including the force of friction) is 10 J.

Next, we can use the work-energy principle again to find the work done on the block by the applied force:

W_applied = F*d*cos(theta) 
W_applied = 10 N * 5.0 m * cos(37°) 
W_applied = 39.3 J

Finally, we can use the work-energy principle once more to find the work done on the block by the force of friction:

W_friction = W_net - W_applied 
W_friction = 10 J - 39.3 J 
W_friction = -29.3 J

Since the force of friction opposes the block's motion, the work done by the force of friction is negative. Therefore, the best answer is C)−68 J, which is the closest to -29.3 J.

A 40-Kg Block Is Lowered Down a 37° Incline a Distance