Question

How much force Fm must an athlete’s biceps apply to a 0.38m forearm to support a 39.2N weight held at 90 degrees? Assume that the forearm weight is 21.56N and that muscle is attached to the bone 0.05m from the joint.

Answer 1

Answer on Question #72486-Physics-Other

How much force Fb must an athlete's biceps apply to a 0.38m forearm to support a 39.2N weight held at 90 degrees? Assume that the forearm weight is 21.56N and that muscle is attached to the bone 0.05m from the joint.

Solution

From the equilibrium:

$$F _ {b} = W _ {a} + W _ {b} + F _ {e}$$ $$F _ {e} r _ {1} = W _ {a} (r _ {2} - r _ {1}) + W _ {b} (r _ {3} - r _ {1})$$ $$F _ {b} = W _ {a} + W _ {b} + W _ {a} \left(\frac {r _ {2}}{r _ {1}} - 1\right) + W _ {b} \left(\frac {r _ {3}}{r _ {1}} - 1\right)$$ $$F _ {b} = \frac {W _ {a} r _ {2} + W _ {b} r _ {3}}{r _ {1}} = \frac {(21.56)(0.19) + (39.2)(0.38)}{0.05} = 380 \, \text{N}.$$

Answer: 380 N.

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