A block is pulled at constant speed along a rough level surface by a rope that makes an angle of 30° with respect to the horizontal. The applied force along the rope is . The force of kinetic friction between the block and the surface is 10 N.
-Complete the following statement: The magnitude of the normal force could be reduced by
A)increasing the speed of the block.
B)decreasing the coefficient of kinetic friction.
C)decreasing the velocity of the block.
D)decreasing the angle made by the rope.
E)increasing the angle made by the rope.

Question

A block is pulled at constant speed along a rough level surface by a rope that makes an angle of 30° with respect to the horizontal. The applied force along the rope is . The force of kinetic friction between the block and the surface is 10 N. 
-Complete the following statement: The magnitude of the normal force could be reduced by
A)increasing the speed of the block. 
B)decreasing the coefficient of kinetic friction. 
C)decreasing the velocity of the block. 
D)decreasing the angle made by the rope. 
E)increasing the angle made by the rope.

Quizplus · Accepted Answer

The normal force is perpendicular to the surface and acts to counteract the weight of the block. As the angle between the rope and the horizontal increases, the component of the applied force parallel to the surface decreases, which reduces the force pushing down on the block and consequently reduces the normal force. Therefore, increasing the angle made by the rope (Choice E) would reduce the normal force. None of the other choices would have an effect on the normal force.

A Block Is Pulled at Constant Speed Along a Rough