72. assignment (force in the knee joint)

During strenuous exercise it is possible to exert forces to the joints that are ten times greater than the weight being supported when not in motion. The coefficients of friction for joints are generally very small - for this problem, assume the coefficient of static friction in a knee joint is 0.016, while for kinetic friction it is 0.015.

m = 69 kg

 

(A) What is the frictional force in the knee joint of a person who is standing still and supporting 69 kg of her mass on a knee?

 

(B) What is the maximum force of friction if this person begins strenuous exercise?

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