In the figure,the horizontal lower arm has a mass of 2.8 kg and its center of gravity is 12 cm from the elbow joint pivot.How much force F_M must the vertical extensor muscle in the upper arm exert on the lower arm to hold a 7.5 kg shot put? A) 100 N B) 500 N C) 750 N D) 1000 N E) 1500 N

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Quizplus · Accepted Answer

Firstly, we need to find the weight of the lower arm which is given by: weight = mass × gravity weight = 2.8 kg × 9.8 m/s² weight = 27.44 N The weight of the shot put can be found in the same way: weight = mass × gravity weight = 7.5 kg × 9.8 m/s² weight = 73.5 N We can now find the force required by using the principle of moments: force × distance = weight(lower arm) × distance(lower arm) + weight(shot put) × distance(shot put) force × 0.12 m = 27.44 N × 0.12 m + 73.5 N × 0.45 m force = (27.44 N × 0.12 m + 73.5 N × 0.45 m) / 0.12 m force ≈ 1000 N Therefore, the force F_M that the vertical extensor muscle in the upper arm must exert on the lower arm to hold the shot put is approximately 1000 N, which is option D.

In the Figure,the Horizontal Lower Arm Has a Mass of 2.8