Polly is pushing a box across the floor with a force of 30 N. The force of gravity is –8 N, and the normal force is 8 N. Which value could describe the force of friction if Polly could not move the box?

A.)–30 N
B.)–8 N
C.)8 N
D.)30 N

Question

Polly is pushing a box across the floor with a force of 30 N. The force of gravity is –8 N, and the normal force is 8 N. Which value could describe the force of friction if Polly could not move the box?

A.)–30 N
B.)–8 N
C.)8 N
D.)30 N

Vocaloid · Answer

In order for Polly not to be able to move the box, the force of friction must “cancel out” the applied force 30N. In other words the sum of the applied force + friction force must be 0.

Which number, when added to 30N, sums to 0?