When you lift an object by moving only your forearm, the main lifting muscle in
ID: 1295567 • Letter: W
Question
When you lift an object by moving only your forearm, the main lifting muscle in your arm is the biceps. Suppose the mass of a forearm is 1.40kg . If the biceps is connected to the forearm a distance dbiceps = 3.00cm from the elbow, how much force Fbiceps must the biceps exert to hold a 650g ball at the end of the forearm at distance dball = 31.0cm from the elbow, with the forearm parallel to the floor? How much force Felbow must the elbow exert? (Figure 1)
Determine the sign (+ or ?) of the torque about the elbow caused by the biceps, ?biceps, the sign of the weight of the forearm, ?forearm, and the sign of the weight of the ball, ?ball.
Explanation / Answer
applying the torque equation about the arm
= Tbiceps + T mg + T ball = 0
= - 0.03* F biceps + [ 0.155 * 9.8 * 1.4 ] + [ 0.31* 0.65 * 9.8 ]
= F biceps = 4.1013 / 0.03
= 136.71 N
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