FM/19 P12 Q12

A fairground ride consists of four carriages connected to a central vertical pole, as shown in the
following view from above.
A motor rotates the central pole about its axis. This results in the four carriages each moving
along a circular path.
The distance from the middle of each carriage to the centre of the pole is 3.20 m. When they are
moving, each carriage experiences an air resistance force of 85.0 N. Assume that there are no
other significant resistive forces.
Which torque does the motor need to apply to the pole to keep the system rotating at constant
maximum speed?