The coefficients of static and kinetic friction between a 3.0-kg box and a horizontal desktop are 0.40 and 0.30,respectively.What is the force of friction on the box when a 15-N horizontal push is applied to the box?
A)12 N
B)8.8 N
C)15 N
D)6.0 N
E)4.5 N

Question

Quizplus · Accepted Answer

Firstly, we need to determine if the box will move or not. To do this, we compare the force of friction to the applied force 15 N:

Maximum force of static friction = coefficient of static friction × normal force
= 0.40 × (3.0 kg × 9.81 m/s²)
= 11.76 N

Since the applied force of 15 N is greater than the maximum force of static friction, the box will move.

The force of kinetic friction will then come into play, given by:

Force of kinetic friction = coefficient of kinetic friction × normal force
= 0.30 × (3.0 kg × 9.81 m/s²)
= 8.83 N

Therefore, the force of friction on the box is 8.83 N, which is closest to option B (8.8 N).

The Coefficients of Static and Kinetic Friction Between a 3