The maximum mass m_1 that a person can hold in a hand when the arm is positioned

Question

The maximum mass m_1 that a person can hold in a hand when the arm is positioned with a 105 degree angle at the elbow as shown in is 21 kg. Assume the forearm and hand have a total mass of m_2 = 3 kg with a center of gravity that is 15 cm from the elbow, and that the biceps muscle attaches 5 cm from the elbow. a. What type of lever is illustrated in the figure? b. Consider the arm keeps a horizontal position and apply the rotational equilibrium condition to determine the maximum force F that the biceps muscle exerts on the forearm?

Explanation / Answer

a) third class lever

third class lever include fishing rods, arms, hammer

b) weightball = 21 * 9.8 = 205.8 N

weightforearm = 2 * 9.8 = 19.6 N

pivot point be at the elbow

Torqueball = 205.8 * 35 * 10-2 = 72.03

Torqueforearm = 19.6 * 15 * 10-2 = 2.94

Total torque = 72.03 + 2.94 = 74.97 N.m

Counter clockwise torque = Fmax * sin 105 * 5 * 10-2

Fmax * sin 105 * 5 * 10-2 = 74.97

Maximum force Fmax = 1550 N

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