? asked in Science & MathematicsPhysics · 2 years ago

As you hold your leg in this position, the upper leg exerts a force on the lower leg at the knee joint. What is the magnitude of this force?

If you stand on one foot while holding your other leg up behind you, your muscles apply a force to hold your leg in this raised position. We can model this situation as in (Figure 1). The leg pivots at the knee joint, and the force that holds the leg up is provided by a tendon attached to the lower leg as shown. Assume that the lower leg and the foot have a combined mass of 3.2kg, and that their combined center of gravity is at the center of the lower leg.


What is the direction of the force exerted by the upper leg on the lower leg at the knee joint?

horizontally leftward

vertically downward

horizontally rightward

vertically upward

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2 Answers

  • Jeff
    Lv 5
    2 years ago

    Torque is 'twist' whomever made the diagram needs schooled.

  • 2 years ago

    You've got a third-class lever with the fulcrum at the knee joint, an upward force to be found 5.0 cm away from the fulcrum, and a downward force of 3.2 kg at 25 cm from the fulcrum.

    (3.2 kg x 25 cm) / 5 cm = 16 kg

    vertically upward (If there was any question, biologists can tell you muscles exert no force except by contraction.)

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