A turning moment of 100 N·m is applied to a shaft through a wheel of radius 50 cm. The minimum normal force needed at the brakes to prevent rotation is______ × 10² N. The coefficient of friction is 0.25.

Question

G1 Physics · Accepted Answer

The applied turning moment is 100 N·m. Two brake pads act tangentially at radius R=0.50 m, and each can provide friction µF, so resisting torque is 2(µF)R. Set 2µFR=100: F=100/[2(0.25)(0.50)]=400 N=4×10² N. Hence the integer answer is 4.