A weight lifter does a series of arm raises while holding a 7.50 kg weight. Her

Question

A weight lifter does a series of arm raises while holding a 7.50 kg weight. Her forearm (including the hand) starts out horizontal and pivots to a vertical position about her elbow. The mass of the lower arm plus hand is 5.00 kg, uniformly distributed along its 35.0cm length.



With each arm raise, by how much does the center of mass of her forearm (including her hand and the weight) rise?



What is the change in its gravitational potential energy with each arm raise?



please provide step by step for the answers

Explanation / Answer

Position of COM

5 x 0.175 + 7.5 x .35 / 12.5 = 28 cm

a) Rise in COM = Position of COM horizontally

= 28 cm (As the weight is uniformly sistributed)

b) Change in GPE

mgh

= 12.5 x 9.8 x (28 x 10-2)

= 34.3 J

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