The diagrams below show the application of an external force F on a block of mass m resting on a horizontal surface. In which diagrams) does the block experience the smallest normal force?
A) Both 1) and 3)
B) Only 1)
C) Only 2)
D) Only 3)
E) Only 4)

Question

The diagrams below show the application of an external force F on a block of mass m resting on a horizontal surface.  In which diagrams) does the block experience the smallest normal force?
A) Both 1) and 3) 
B) Only 1) 
C) Only 2) 
D) Only 3) 
E) Only 4)

Quizplus · Accepted Answer

The normal force on the block is the force exerted by the surface on the block perpendicular to the surface. In diagram 2), the external force F is acting perpendicular to the surface, which means there is no component of force acting in the vertical direction. Therefore, the normal force experienced by the block in diagram 2) will be equal to its weight, which is the smallest compared to the other diagrams where the force F has a component acting in the vertical direction. In diagrams 1) and 3), the force F is at an angle to the surface, causing a vertical component of the force which increases the normal force. In diagram 4), the force F is acting downwards, which will also increase the normal force.

The Diagrams Below Show the Application of an External Force