Chapter 10, Problem 054 Flying Circus of Physics In a judo foot-sweep move, you

Question

Chapter 10, Problem 054 Flying Circus of Physics In a judo foot-sweep move, you sweep your opponent's left foot out from under him while pulling on his gi (uniform) toward that side. As a result, your opponent rotates around his right foot and onto the mat. The figure shows a simplified diagram of your opponent as you face him, with his left foot swept out. The rotational axis is through point O. The gravitational force Fg on him efectively acts at his center of mass, which is a horizontal distance d-29 cm from point o. His mass is 67 kg, and his rotational inertia about point o is 65 kgm2. What is the magnitude of his initial angular acceleration about point o if your pull F a on his gi is (a) negligible and (b) horizontal with a magnitude of 300 N and applied at height h 1.4 m? Assume free-fall acceleration to be equal to 9.81 m/s (a) Number Units b) Number Units

Explanation / Answer

a)

Torque

T=mgd=67*9.8*0.29=190.61 N-m

angular acceleration

alpha =T/I =190.61/65 =2.932 rad/sec2

b)

Net Torque

Tnet =67*9.81*0.29 +300*1.4

Tnet=610.61 N-m

angular acceleration

alpha =610.61/65

alpha=9.4 rad/sec2

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