Kevin S. Huang

2013: Problem 22

Topic: Dynamics
Concepts: Statics

Solution:

Choosing the ankle joint as the pivot point, only the normal force from the ground and tension in the Achilles tendon contribute to the torque:

T(5\,\mathrm{cm})=N(20\,\mathrm{cm})

Since the student is standing on a single toe, $N=mg$ so we have

T=4N=4mg=4(60\,\mathrm{kg})(10\,\mathrm{m/s^2})=2400\,\mathrm{N}

so the answer is D.

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2013, F=ma Exam

Fma: Dynamics, Statics

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