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# Torque and hydraulic brake system question. (Homework help.) :)?

Figure P9.25 shows the essential parts of a hydraulic brake system. The area of the piston in the master cylinder is 1.75 cm2, and that of the piston in the brake cylinder is 6.4 cm2. The coefficient of friction between shoe and wheel drum is 0.50. If the wheel has a radius of 32 cm, determine the frictional torque about the axle when a force of 39 N is exerted on the brake pedal.To see image I will email it to you.I looked on yahoo answers before and someone gave answers that didn‘t make sense to me. They said to find the normal force (Fn) to find the force of friction (Ff) and that the torque (T) will be equal to Ff*r*(sin theta).They said Fn Force exerted on brake and that Ff Fn* coefficient of friction/(area of master cylinder + area of brake cylinder).It seems to me that they are confusing pressure with force. Because doesn‘t PressureForce/Area??? Please explain how to use the radius of each cylinder and why we use it in that way.