Question

The total mass of the arm shown in (Figure 1) is 3.5 kg . The location of the center of mass of the arm is shown, FM is the force exerted by the deltoid muscle on the upper arm, and FJ is the normal force from the shoulder joint on the upper arm.

FM 15° -12 cm 74 cm

Part A

Determine the magnitude of the force required from the deltoid muscle to hold up the outstretched arm in the position shown.

Part B

Suppose this person wanted to raise their arm above their head, rotating their arm upward from the position shown. If they move their arm with an angular acceleration of 4.3 rad/s2 , what is the magnitude of the force the deltoid muscle must provide? You may approximate the arm as a long, thin, uniform rod.

Answer 1

@ X-sino formula for net torque is, T= x Fisino Fr= mad = 3.5 (9.8) (0.24) 265 N (0.12) sinis Ther - It Fm (0.12) Sinis -3.5 (9.8) (0:24) = 43.5) (0:483643) FM = 302:2)