## College Physics (4th Edition)

The correct answer is: B. $25~N$
The two pads provide a total retarding force of 20 N. Since there are two pads, each pad provides a retarding force of 10 N. We can find the normal force $F_N$ of each pad on the wheel: $F_N~\mu_k = 10~N$ $F_N = \frac{10~N}{\mu_k}$ $F_N = \frac{10~N}{0.4}$ $F_N = 25~N$ The correct answer is: B. $25~N$