2048_Fall09_Exam2

# 1 4 ω 3 2 ω 3 ω 2 4 2 ω 5 3 ω 2 11 a 100 n

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that is at the center of the disk what is the new angular velocity of the mouse-disk system? (1) 4 ω/ 3 (2) ω (3) ω/ 2 (4) 2 ω (5) 3 ω/ 2 11. A 100-N uniform plank leans against a frictionless wall as shown. The magnitude of the torque (about the point P) applied to the plank by the wall is: (1) 150 N · m (2) 100 N · m (3) 500 N · m (4) 200 N · m (5) 75 N · m 12. A 0.5-kg rubber ball is dropped from rest a height of 19.6 m above the surface of the Earth. It strikes the sidewalk below and rebounds up to a maximum height of 4.9 m. The magnitude of the impulse due to the collision with the sidewalk is: (1) 14.7 N · s (2) 4.9 N · s (3) 19.6 N · s (4) 8.3 N · m (5) 16.6 N · m 13. A wheel initially ( t = 0) has an angular velocity of 18 rad/s. It has a constant angular acceleration with a magnitude 2 rad/s 2 and at t = 0 the angular velocity is decreasing. At what time t is the angular velocity equal to 18 rad/s in the direction opposite to the initial angular velocity? (1) 18 s (2) 3 s (3) 6 s (4) 9 s (5) 36 s 14. An astronaut is being tested in a centrifuge. The centrifuge has a radius R and, in starting from rest at t = 0, rotates according to θ ( t ) = (0 . 5 rad/s 2 ) t 2 . At what time t > 0 is the magnitude of the tangential acceleration equal to the magnitude of the radial acceleration ( i.e. , centripetal acceleration)? (1) t = 1 s (2) t = 2 s (3) t = 0 . 5 s (4) never (5) need to know the radius R 15. A single force acts on a particle located on the positive y -axis a distance d from the origin ( i.e. , at the point P = ( x, y, z ) = (0 , d, 0)). The torque about the origin is non-zero and points in the positive x direction. The force must be: (1) in the positive z direction (2) in the negative z direction (3) in the positive x direction (4) in the negative x direction (5) in the positive y direction 16. A 0.5-kg particle-like object moves in a plane with velocity ~v = (30 m/s ) ˆ i + (60 m/s ) ˆ j . What is the magnitude of its angular momentum relative to the origin when it passes through the point with ( x, y, z ) coordinates of (2m, 4m, 0)? (1) zero (2) 6.0 J · s (3) 12.0 J · s (4) 150 J · s (5) 164.3 J · s

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77777 77777 17. Near the surface of the Earth a block of mass M and initial velocity 16.97 m/s is sliding to the right along the x -axis as shown. The surface is frictionless for x < 0. At x = 0 the block encounters a 45 incline ramp. If the block
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