An athlete is doing a knee extension exercise using a 100N dumbbell strapped to

Question

An athlete is doing a knee extension exercise using a 100N dumbbell strapped to her ankle, 40 cm from the knee joint. The athlete holds her leg so that the horizontal distance from her knee to the dumbbell is 30 cm. a) For this position, what torgue is created by the dumbbell about her knee joint axis? * I know that M=F*r sin(x) but I'm unsure of how to find the correct theta. This should be the theta from applied F to moment arm I believe b)If the moment arm of the knee extensor muscles is 4cm about the knee joint axis, what amount of force must these muscles produce to hold the leg in the position described? (Ignore the weight of the leg).

Explanation / Answer

Since gravity works vertically, the 30 cm distance should be used since it will be perpendicular to the force of gravity working through the weight. T =F d = 100N(0.30m) = 30 Nm ANSWER ========================== F= 30Nm/ 0.04m = 750 N ANSWER

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