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exam 3 key

exam 3 key - Question 21 A weightlifter is attempting to...

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Question 21 A weightlifter is attempting to lift a 200 N barbell. The moment arm of the barbell about the elbow joint is 40 cm. The moment arm of the elbow flexor muscles is 4 cm. How much force must be produced by these muscles to hold the 200 N barbell in static equilibrium? (2 pts) Given Answer: T=Fr T=(200N)(0.4m)= 80Nm (torque on the elbow joint produced by the barbell) magnitude of the torque produced by barbell = magnitude of the torque produced by elbow 80Nm = force of muscle x (0.04m) Force of muscle= 2000N in the direction of the elbow flexion Question 22 points Bill lifts a 1000 N barbell 1.5 m in 1.0 s, while Bob lifts a 1400 N barbell 2.0 m in 2.0 s. Whose lift was more powerful? Explain answer. (2 pts) Given Answer: Bill: P= F(d/t) P= (1000N)(1.5m/1s) P= 1500W Bob: P= F(d/t) P= (1400N)(2m/2s) P= 1400W Bill's lift was more powerful because using the power equation P= F(d/t), Bill produced 1500W while Bob produced only 1400W. Bob produced a higher force and performed more work.

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