The deltoid muscle holds the arm outstretched as shown. Arm weight W=30 N acts downward 30 cm horizontally from the shoulder joint. Muscle attachment is 15 cm from the joint and muscle tension makes 20° with horizontal. Find tension in N.
Take moments about the shoulder joint, eliminating its reaction. Muscle moment is T×.15×sin20°, balancing the weight moment 30×.30=9 N m. Thus T=9/[.15sin20°]≈175.43 N. Choose D. Only the vertical component of muscle tension contributes to this moment.
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