Question

A person lifts a dumbbell of weight Wd (see below). Their arm weighs Wa. The deltoid muscle is attached to the arm at an angle as shown and supplies a force Fd. The freebody diagram below illustrates the distances where the various forces act on the arm. Write an expression for Fd in terms of Wa, wd, L1, L2, L3 and e. Write and expression for the total reaction force R that the shoulder joint applies to the left end of the arm (Note that Ris a vector). Deltoid Dumbbell Fd muscle Rx wa Ry Shoulder joint

Answer 1

FBD of arm. Ry n fasino A लन fRy Wd WQ L L -23 Efe = 0 RC For loso - {fy :0 → Ry + For Smo z Wąt Wing z EMA =0 (moment about left end nd) Fa SmeX41 WaLa - Wd L₂ = 0 3 Fo Wa Sme () + Wa ( 4 ) Answer sme put in equation 0 Rr = For loso Wh tan Wd 143) + tano from eacuation ③ Ry Wat wil Fa smo = wat was = {wal 4 ) t W ( 1 } wal.-) + woll-up) Ry Hence, Total reactrm R Pult Ry l2)= TR+CRY)2 Ang