physics
posted by Samuel on .
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 Newtonmeters, 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?

Torque is not measured in Newtons. You failed to include g as a factor to convert mass to weight.