Question

A box with a mass of 15.0 kg is being pushed on a level surface with a horizontally applied force. It just starts to slide when 40.0 N is applied and will continue to slide if 35.0 N is applied to the box. What is the coefficient of static friction (us) of these surfaces?

A) 0.25
B) 0.50
C) 0.33
D) 0.75

Answer 1

The coefficient of static friction is found by dividing the maximum applied force before movement (40.0 N) by the normal force (147 N), resulting in a value closest to 0.33, which corresponds to option C.

Step-by-step explanation:

The static frictional force opposing motion will equal the maximum force applied just before the box starts to slide. To calculate the static coefficient of friction, use the equation:fmax = us * N. where fmax is the maximum static frictional force, us is the coefficient of static friction, and N is the normal force. In this case, N is equal to the weight of the box, N = mass * g, where g = 9.8 m/s2, and so N = 15.0 kg * 9.8 m/s2 = 147 N. Given that fmax is 40.0 N, you can solve for us as follows: us = fmax / N = 40.0 N / 147 N = 0.272. Looking at the choices provided, the coefficient of static friction (us) is closest to C) 0.33 when rounded to two decimal places.