# physics

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

---------------------
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?

1. 👍 0
2. 👎 0
3. 👁 113
1. Torque is not measured in Newtons. You failed to include g as a factor to convert mass to weight.

1. 👍 0
2. 👎 0
posted by drwls

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