The center of mass of a system of particles remains

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4. The center of mass of a system of particles remains at the same place if: (a) it is initially at rest and the external forces sum to zero 4 (b) the sum of the external forces is less than the maximum force of static friction (c) it is initially at rest and the internal forces sum to zero (d) no friction acts internally (e) none of the above 5. A picture is to be hung from the ceiling by means of two wires. Order the following arrangements of the wires according to the tension in wire B, from least to greatest. A B cm I A B cm II A B cm III 6. A particle is in simple harmonic motion with period T . At time t 0 it is at the equilibrium point. At which of the following times is it furthest from the equilibrium point? 3
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7. The fan shown has been turned off and is slowing as it rotates clockwise. X It slows down fast, so that the absolute value of the rate of change of angular velocity | { dt | is approximately equal to the square of the angular velocity ω 2 . The direction of the acceleration of the point X on the fan tip is best described by: 8. An object is dropped from rest. Which of the five following graphs correctly represents its motion? The positive direction is taken to be downward. (a) t v 4 (b) t v (c) t v (d) t x (e) t v 4
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9. A boat is able to move through still water at 20 m/s. It makes a round trip to a town 3.0 km upstream. If the river flows at 5 m/s, the time required for this round trip is: 10. A girl wishes to swim across a river to a point directly opposite as shown. She can swim at 2 m/s in still water and the river is flowing at 1 m/s. Start Finish θ 1 m/s At what angle with respect to the line joining the starting and finishing points should she swim? 11. A forward force acting on the axle accelerates a rolling wheel on a horizontal surface. If the wheel does not slide the frictional force of the surface on the wheel is: 5
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