Two thin circular discs, each of mass 2 kg and radius 10 cm, are joined by a massless rod of length 20 cm and roll without slipping on an accelerating truck. The truck acceleration is 9 m/s². Which option correctly gives both (i) the friction on each disc and (ii) the frictional torque about the object centre O?

Question

G1 Physics · Accepted Answer

The two discs roll without slipping on the accelerating truck. For each disc, translation in the truck frame and rotation about its centre give the friction needed for a=9 m/s². Solving gives friction 6 N on each disc. The torque of friction about the object’s centre O has components from the disc offset and contact radius, giving τ⃗=-0.6ĵ±0.6k̂ N·m. Hence option A.