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Question

An athlete in a gym applies a constant force of 50 N to the pedals of a bicycle to keep the rotation rate of the wheel at 10 rev/s. The length of the pedal arms is 30 cm. What is the power delivered to the bicycle by the athlete?

Solution

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We know that :

τ=rF\tau = r_{\perp} F

And the power :

P=τωP = \tau \omega

From the kinematics of the rotational motion \textbf{the kinematics of the rotational motion } we know that :

[10×60  revmin2π  radrev1min60  s=62.83  rad/s]\left[ \dfrac{10 \times 60\; \text {rev}}{\text{min}} \cdot \dfrac{2 \pi\; \text{rad}}{\text{rev}} \cdot \dfrac{1 \text{min}}{60\; \text{s}} = 62.83\; \mathrm{rad/s} \right]

Where :

  • FF is the force acting on the pedals .
  • rr is the radius of the pedals .
  • ω\omega is the angular velocity of the pedals .
  • τ\tau is the torque acting on the pedals due to the force .

Givens\textbf{Givens} : r=0.3 mr_{\perp} = 0.3 \ \text{m} , F=50 NF= 50 \ \mathrm{N} and ω=62.83 rad/s\omega = 62.83\ \mathrm{rad/s}.

Plugging \textbf{Plugging } known information into to get :

τ=rF=0.3×50=15P=τω=15×62.83=942.45\begin{align*} \tau & = r_{\perp} F \\ &= 0.3 \times 50 \\ &= 15 \\ P &= \tau \omega \\ &= 15 \times 62.83\\ &=942.45 \end{align*}

P=942.45 W\boxed{P = 942.45 \ \text{W} }

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