A 3.0 kg bobbin consists of a central cylinder of radius 5.0 cm and two end plates each of radius 6.0 cm. It is placed on a slotted incline, where friction is sufficient to prevent sliding. A block of mass 4.5 kg is suspended from a cord wound around the bobbin and passing through the slot under the incline. If the bobbin is in static equilibrium, what is the angle of tilt of the incline?

Question

G1 Physics · Accepted Answer

The bobbin is in static equilibrium, so translation along the incline and torque about its centre both vanish. Write T-Mg sinθ-f=0 and T × inner radius=f outer radius; the hanging block gives T=4.5g. Using inner radius 5 cm and outer radius 6 cm yields θ=30°. Hence the numerical answer is 30.