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Question :
21. A uniform beam of length 3.00 m and weight : 2102170

21. A uniform beam of length 3.00 m and weight 100 N is mounted on an axle at one end perpendicular to the length of the beam. A rope is attached to the end of the beam at the other end from the axle, and the beam is lifted by the rope so that the beam makes an angle of 30.0? with the horizontal. If the rope is straight up, what magnitude torque does it supply about the axle?

A. 300 N·m

B. 150 N·m

C. 130 N·m

D. 75.0 N·m

22. A uniform beam of length 4.0 m and weight 100 N is mounted on an axle at one end perpendicular to the length of the beam. A rope is attached to the end of the beam at the other end from the axle and the beam is lifted by the rope so that the beam makes an angle of 30? with the horizontal. What is the tension in the rope if it is straight up?

A. 50 N

B. 87 N

C. 100 N

D. 200 N

23. The quantity "moment of inertia" (in terms of the fundamental quantities of mass, length, and time) is equivalent to:

A. ML^{2}T^{-2}.

B. ML.

C. ML^{2}.

D. ML^{-1}T^{-2}.

24. A 4.2-kg mass is placed at (3.0, 4.0) m. Where can an 8.4-kg mass be placed so that the moment of inertia about the *z*-axis is zero?

A. (-3.0, -4.0) m

B. (-6.0, -8.0) m

C. (-1.5, -2.0) m

D. There is no position giving this result.

25. A 4.0-kg mass is placed at (3.0, 4.0) m, and a 6.0-kg mass is placed at (3.0, -4.0) m. What is the moment of inertia of this system of masses about the *x*-axis?

A. 160 kg?m^{2}

B. 90 kg?m^{2}

C. 250 kg?m^{2}

D. 32 kg?m^{2}