## College Physics (4th Edition)

(a) The normal force applied to each side of the rotor is $30~N$ (b) $\tau = 5.76~N\cdot m$
(a) We can use Pascal's principle to find the normal force $F_2$ applied to each side of the rotor: $\frac{F_2}{A_2} = \frac{F_1}{A_1}$ $F_2 = \frac{A_2~F_1}{A_1}$ $F_2 = \frac{(12.0~cm^2)~(7.5~N)}{3.0~cm^2}$ $F_2 = 30~N$ The normal force applied to each side of the rotor is $30~N$ (b) We can find the total torque on the rotor due to the two pads: $\tau = 2\times~(r~F_2~\mu_k)$ $\tau = (2)(0.12~m)(30~N)(0.80)$ $\tau = 5.76~N\cdot m$