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An empty cage being lowered in a mine hoist represents

  • A.a case where the load torque is proportional to the square of the speed
  • B.a case in which no torque of any kind is required from the motor
  • C.a case where the motor must drive the load down
  • D.a case in which gravity alone will lower the cage at a controlled speed

Answer: C

The friction of the guides and the weight of the balancing rope can exceed the weight of the empty cage, so the motor has to push it downwards. That is why a hoist drive must be capable of operating in all four quadrants.

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