Question

Fig.7.19 shows a bicycle pedal. Suppose your foot is at the top and you are pressing the pedal downwards. 

(i) What torque do you produce? 

(ii) Where should your foot be for generating maximum torque? 

Fig.7.19 : A bicycle pedal (a) at the top when τ = 0; (b) when τ is maximum

Answer 1

 (i) When your foot is at the top, the line of action of the force passes through the centre of the pedal. So, θ = 0, and τ = Fr sinθ = 0.

(ii) To get maximum torque, sinθ must have its maximum value, that is θ must be 90º. This happens when your foot is at position B and you are pressing the pedal downwards.