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Unformatted text preview: QUESTION 1* A 12 kg block moves in the xdirection at 28 m/s, and a 24 kg block moves in the ydirection at 8.0 m/s. Find the velocity of their center of mass. (a) ( V x , V y ) = (6.3 m/s, 1.6 m/s) (b) ( V x , V y ) = (2.8 m/s, 4.9 m/s) (c) ( V x , V y ) = (8.6 m/s, 2.6 m/s) (d) ( V x , V y ) = (9.3 m/s, 5.3 m/s) (e) ( V x , V y ) = (4.6 m/s, 1.4 m/s) QUESTION 2** A light automobile has a speed of 45 miles per hour in the + x direction and a heavy truck has a speed of 30 miles per hour in the  x direction. What is the relative speed s cm at which they approach one another in the centerofmass system? (a)  s cm  &lt; 75 mph (b)  s cm  = 75 mph (c)  s cm  &gt; 75 mph QUESTION 3** This and the next two questions refer to the following situation: A 4.0 kg circular disk slides in the xdirection on a frictionless horizontal surface with a speed of 5.0 m/s. It collides with an identical disk that is at rest before the collision. The collision is elastic. Disk 1 goes off at an angle of 60 with respect to the xdirection. Disk 2 goes off at an angle of 30 with respect to the xdirection. Treat the disks as point objects and ignore the possible rotations of the disks. Which one of the following statements is correct? (a) Disk 1 has the greater kinetic energy after the collision. (b) Disk 2 has the greater kinetic energy after the collision. (c) The kinetic energies of the two disks are equal after the collision. QUESTION 4*** Find the speed of disk 2. (a) 2.5 m/s (b) 2.8 m/s (c) 3.3 m/s (d) 3.9 m/s (e) 4.3 m/s QUESTION 5* Find the sum of the kinetic energies of disk 1 and disk 2 after the collision. (a) 0 J (b) 25 J (c) 50 J (d) 75 J (e) 100 J QUESTION 6* This and the next question refer to the following situation: In a Physics 211 laboratory experiment one end of a string is tied to a cart. The other end of the string is tied to a force probe that is fixed to the track. The cart is free to move on the track. Initially the string is slack. The cart is given a velocity v o and the magnitude of the momentum of the cart is 0.42 kg m/s. The experimental setup is shown below. The string becomes taut, and a force is exerted on the cart by the string. The string then becomes slack again. The force on the cart is measured as a function of time by the force probe. The data from the force probe are shown below. The integral of force on the cart with respect to time is 0.66 kg m/s....
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This note was uploaded on 05/04/2011 for the course PHYS 211 taught by Professor Liss during the Spring '08 term at University of Illinois at Urbana–Champaign.
 Spring '08
 Liss
 Center Of Mass, Mass

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