You are holding a 12lb weight in your hand which is 23 inche

You are holding a 12lb weight in your hand which is 23 inches from your elbow and parallel to the floor. The COM of your arm is 10 inches from the elbow and 6.5 lbs. Assuming the muscular reaction force is pulling straight upwards from your arm 2.5 inches away from your elbow joint, the resultant force would be ??how many lbs. (repot to 1 decimal place.

Solution

COM is 10 inches from the elbow is 6.5 lbs ---F1

12lb weight in your hand which is 23 inches from your elbow ---- F2

Let the resultant force be Fr

The net torque is zero.

F1*10 + F2*23 + Fr*2.5 =0

6.5*10 + 12*23 + Fr*2.5 =0

Fr = -136.4 lb is the resultant force