2048_Fall09_Exam2

# The weight of w is 1 50 n 2 75 n 3 60 n 4 40 n 5 25 n

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an unknown weight W instead results in “30” on the scale. The weight of W is (1) 50 N (2) 75 N (3) 60 N (4) 40 N (5) 25 N 5. A 0.50-kg block attached to an ideal spring with a spring constant of 80 N/m oscillates on a horizontal frictionless surface. When the spring is 4 cm longer than its equilibrium length, the speed of the block is 0.50 m/s. The greatest speed of the block is: (1) 0.71 m/s (2) 0.23 m/s (3) 0.32 m/s (4) 0.55 m/s (5) 0.93 m/s 6. A 0.5-kg particle moves along the x axis under the influence of a conservative force. The potential energy is given by U ( x ) = (8 J/m 2 ) x 2 + (2 J/m 4 ) x 4 , where x is the coordinate of the particle in meters. If the particle has a kinetic energy of 6 J when it is at x = 1 m, its speed when it is at the origin is: (1) 8 m/s (2) 0 m/s (3) 5 m/s (4) 6 m/s (5) 16 m/s 7. A particle is released from rest at the point x = a and moves along the x axis subject to the potential energy function U ( x ) as shown in the figure. The particle (1) moves to a point x = e , then moves to the left (2) moves to a point x = e , stops, and remains at rest (3) moves to infinity at varying speed (4) moves to x = b , where it remains at rest (5) moves to x = e and then to x = d , where it remains at rest 8. A particle moves along the x-axis under the influence of a conservative force. The potential energy is given by U ( x ) = (6 J/m 2 ) x 2 - (24 J/m ) x , where x is the coordinate of the particle. At what value of the position x is the force on the particle equal to zero? (1) x = 2 m (2) x = 4 m (3) x = 6 m (4) x = 0 (5) The force is not zero at any value of x

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77777 77777 9. At the same instant that a 0.50-kg ball is dropped from 25 m above Earth, a second ball, with a mass of 0.25 kg, is thrown straight upward from Earth’s surface with an initial speed of 15 m/s. They move along nearby lines and pass without colliding. What is the velocity of the center-of-mass of the two-ball system 2 seconds after the balls are released? (1) 14.6 m/s, downward (2) 14.6 m/s, upward (3) 19.6 m/s, downward (4) 19.6 m/s, upward (5) 5.0 m/s, upward 10. A mouse of mass M lies on the rim of a uniform disk of mass 6 M that can rotate freely about its center like a merry-go- round. Initially the mouse and disk rotate together with an angular velocity of ω . If the mouse walks to a new position that is at the center of the disk what is the new angular velocity of the mouse-disk system?
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