An athlete at the gym holds a 3.0 kg ball in his hand. His arm is .70 cm long and has a mass of 4.0 kg. What is the magnitude of the torque about his arm if he holds his arm straight out his side, parallel to the floor. I did T=mgr since theta is zero so both the force of gravity on his arm and ball is down. So 7* 9.8*.70 where the mass is the mass of his arm + mass of the ball. I get 48 N-m but this is wrong the answer is 34 N-m. What am I doing wrong?
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 Recognitions: Homework Help This would by right if all mass of the arm were concentrated in the hand. ehild

 Quote by ehild This would by right if all mass of the arm were concentrated in the hand. ehild
So is .70 m not the center of gravity. I'm so confused ...