Posted by **Samuel** on Monday, October 13, 2008 at 2:28am.

An athlete at the gym holds a 4.33 kg steel ball in his hand. His arm is 75.0 cm long and has a mass of 5.28 kg. What is the magnitude of the torque about his shoulder if he holds his arm straight out to his side, parallel to the floor?

Responses

Physics - bobpursley, Saturday, October 11, 2008 at 9:36pm

The torque has to be the weight of the ball x distance plus the weight of the arm x 1/2 the length of the arm(assuming the cg is at the midpoint).

Is distance 0.75 m?

Responses

physics - drwls, Sunday, October 12, 2008 at 11:35am

What distance? The arm length is 0.75 m, but half of that is 0.375 m

If you want torque in units of Newton-meters, the lengths must be in meters when you do the calculation

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Torque = the weight of the ball x distance plus the weight of the arm x 1/2 the length of the arm

= 4.33 kg x 0.75 m + 5.28 kg x 0.375 m

= 3.2475 + 1.98

= 5.23 N

What am I doing wrong?

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