HW08_Sols_Giancoli

HW08_Sols_Giancoli - Problem Set # 8 Giancoli 4th ed....

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Problem Set # 8 Giancoli 4 th ed. 12.16. ( a ) Calculate the torques about the elbow joint (the dot in the free- body diagram). The arm is in equilibrium. Take counterclockwise torques as positive. ( ) ( ) ( ) ( ) ( ) M 2 M o sin 0 3.3 kg 9.80m s 0.24 m 249.9N sin 0.12 m sin15 250N F d mgD mgD F d ! " = # = $ = = = % ( b ) To find the components of J , F write Newton’s second law for both the x and y directions. Then combine them to find the magnitude. ( ) ( ) ( ) ( ) ( ) ( ) J M J M M J 2 J M 2 2 2 2 J J J cos 0 cos 249.9N cos15 241.4N sin 0 sin 249.9N sin15 3.3kg 9.80m s 32.3N F 241.4N 32.3N 243.6N 240N x x x y y y x y F F F F F F F mg F F F mg F F = " = # = = = = " " = # = " = ° " = = + = + = $ ° % % 12.19. There will be a normal force upwards at the ball of the foot, equal to the person’s weight ( ) N . F mg = Calculate torques about a point on the floor directly below the leg bone (and so in line with the leg bone force, B F ! ). Since the foot is in equilibrium, the sum of the torques will be zero. Take counterclockwise torques as positive. ( ) ( ) ( ) N A 2 A N 2 0 2 2 2 72 kg 9.80m s 1400N F d F d F F mg = " = # = = = = $ The net force in the y direction must be zero. Use that to find B . F N A B B N A 0 2 3 2100N y F F F F F F F mg mg mg = + ! = " = + = + = = # 12.21. ( a ) The pole is in equilibrium, and so the net torque on it
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HW08_Sols_Giancoli - Problem Set # 8 Giancoli 4th ed....

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