Q6.7 Torque (S)
A cyclist of mass 70 kg puts all his weight on each downward moving pedal as he ascends a steep hill. If the diameter of the circle in which the pedals rotate is 40 cm, determine the magnitude and direction of the maximum torque vector he exerts.Hint
Reveal
Solution
Reveal
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Solution
The torque vector always points perpendicular to the bicycle frame, to the left hand side of the bicycle if it is moving forwards. The torque the cyclist exerts is maximum when his weight acts perpendicular to the pedal, in which case τ=mgr where r=0.2 m is the distance of the pedal from the rotation axis, and mg the weight of the cyclist. Taking g=10 ms-2 we find that the magnitude of the torque is τ=140 Nm. |