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Practice_Test_2 - Name 1 Date The coefficient of kinetic...

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Unformatted text preview: Name: 1. Date: The coefficient of kinetic friction: A) is in the direction of the frictional force B) is in the direction of the normal force C) is the ratio of force to area D) can have units of newtons E) none of the above . A forward horizontal force of 12 N is used to pull a 240-N crate at constant velocity across a horizontal floor. The coefficient of friction is: A) 0.5 B) 0.05 C) 2 D) 0.2 E) 20 A crate rests on a horizontal surface and a woman pulls on it with a lO—N force. No matter what the orientation of the force, the crate does not move. Rank the situations shown below according to the magnitude of the frictional force of the surface on the crate, least to greatest. 10M 10M :I 10M 1 2 3 u u u \- bah-plur- Mmqmwh.) p—N—nmm m gases 9 u ‘A car is traveling at 15 m/s on a horizontal road. The brakes are applied and the car skids to a stop in 4.0 s. The coefficient of kinetic friction between the tires and road is: A) 0.38 B) 0.69 C) 0.76 D) 0.92 E) 1.11 Page 1 5. A 400-N block is dragged along a horizonatl surface by an applied force 17" as shown. The coefficient of kinetic friction is m = 0.4 and the block moves at constant velocity. The magnitude of 17" is: A) IODN B) 150N C) 200N D) 290N E) 400 Nb 6. Block A, with a mass of 10 kg, rests on a 35° incline. The coefficient of static friction is 0.40. An attached string is parallel to the incline and passes over a massless, frictionless pulley at the top. The largest mass mg, of block B, attached to the dangling end, for which A begins to slide down the incline is: A) 2.5 kg B) 3.5 kg C) 5.9 kg D) 9.0 kg E) 10.5 kg 7. An object of mass m and another object of mass 2m are each forced to move along a circle of radius 1.0 m at a constant speed of 1.0 m/s. The magnitudes of their accelerations are: A) equal B) hitheratioofx/E :1 C) in the ratio of2: 1 D) in the ratio of4:1 E) zero Page 2 8. 10. 11. 12. One end of a 1.0-m long string is fixed, the other end is attached to a 2.0-kg stone. The stone swings in a vertical circle, passing the bottom point at 4.0 m/s. The tension force of the string (in newtons) at this point is about: A) 0 B) 12 C) 20 D) 32 E) 52 . A coin is placed on a horizontal phonograph turntable. Let N be the normal force exerted by the turntable on the coin, f be the fiicfional force exerted by the turntable on the coin, and f; m be the maximum force of the static friction. The speed of the turntable is increased in small steps. If the coin does not slide, then A) N increases, f increases, and fi, max stays the same B) N increases, f increases, and )2, max increases C) f increases and both N and )2, max stay the same D) N, f, and fi, max all stay the same E) N, fl and fi, max all increase An object moves in a circle at constant speed. The work done by the centripetal force is zero because: A) the displacement for each revolution is zero B) the average force for each revolution is zero C) there is no friction D) the magnitude of the acceleration is zero E) the centripetal force is perpendicular to the velocity A l-kg block is lifted vertically 1 m by a boy. The work done by the boy is about: A) 1 ft lb B) 1 J C) 10 J D) 0.1 J E) zero A particle moves 5 m in the positive x direction while being acted upon by a constant force P= (4 N); + (2 N)_/°— (4 N)§. The work done on the particle by this force is: A) 20 J B) 10 J C) ~20 J D) 30 J E) is impossible to calculate without knowing other forces Page 3 13. 14. 15. 16. 17. Which of the following bodies has the largest kinetic energy? A) Mass 3M and speed V B) Mass 3M and speed 2V C) Mass 2M and speed 3 V D) Mass M and speed 4V B) All four of the above have the same kinetic energy The velocity of a particle moving along the x axis changes from v; to 12;. For which values of v,- and Wis the total work done on the particle positive? A) v: = Smis, vf= Zmr's B) v: = 5W5, vy= —2mi's C) v: = ~5mfs, v;= ~2mx’s D) v.- = —~5m/s, v;= 2mfs E) v,- = —2m/s, Vf= —5m/s The amount of work required to stop a moving object is equal to the: A) velocity of the object B) kinetic energy of the object C) mass of the object times its acceleration D) mass of the object times its velocity E) square of the velocity of the object A 4-kg cart starts up an incline with a speed of 3 m/s and comes to rest 2 m up the incline. The total work done on the cart is: A) 6 J B) 8 J C) 12 J D) 18 J E) impossible to calculate without more information At time t = 0 a 2-kg particle has a velocity in m/s of (4 ms); — (3 nus); At t = 3 5 its velocity is (2 nus); + (3 m/sy“. During this time the work done on it was: A) 4 J B) —4 J C) —12 J D) —40 J E) (4 J); + (36 1);“ Page 4 18. 19. 20. Only if a force on a particle is conservative: A) is particle is conservative when the particle moves exactly once around any closed path B) is it work equals the change in the kinetic energy of the particle C) it obeys Newton‘s second law D) it obeys Newton‘s third law B) it is not a frictional force The graphs below show the magnitude of the force on a particle as the particle moves along the positive x axis from the origin to x = x1. The force is parallel to the x axis and is conservative. The maxium magnitude F1 has the same value for all graphs. Rank the situations according to the change in the potential energy associated with the force, least (or most negative) to greatest (or most positive). F‘ F‘ It F1 F1 Jr1 :13 3‘3 X F1 1 2 3 An elevator is rising at constant speed. Consider the following statements: I. the upward cable force is constant [1. the kinetic energy of the elevator is constant 111. the gravitational potential energy of the Earth-elevator system is constant IV. the acceleration of the elevator is zero V. the mechanical energy of the Earth-elevator system is constant in Hwy—H b—‘Mj—h’l-JJM er-Nw e u u u 599393 u A) all five are true B) only ll and V are true C) onlyIVandVaren-ue D) only I, II, and III are true E) only I, II, and IV are true Page 5 21. The long pendulum shown is drawn aside until the ball has risen 0.5 m. It is then given an initial speed of 3.0 mr’s” The speed of the ball at its lowest position is: (fflflflflflff I A) zero B) 0.89m/s C) 3.1mfs D) 3.7mfs E) 4.3 mfs 22. An ideal spring is used to fire a 15.0-g block horizontally across a frictionless table top. The spring has a spring constant of 20 N/rn and is initially compressed by 7.0 cm. The speed of the block as it leaves the spring is: A) 0 B) 1.9 x 10’3 mfs C) 2.6 x 10‘2 mfs D) 0.39 mfs E) 2.6 m/s 23. A small object of mass m, on the end of a light cord, is held horizontally at a distance r from a fixed support as shown. The object is then released. What is the in the cord when the object is at the lowest point of its swing? l 7’ m A) nag/'2 B) mg C) 2mg D) 3mg E) mgr Page 6 24. A block is released from rest at point P and slides along the frictionless track shown. At point Q, its speed is: ground level A) Zth-hz B) 230“ — hz) C) (ht — h2)f23 D) \(2g(h.—h2) E) (ht - h2)2f28 25. A ball of mass m, at one end of a string of length L, rotates in a vertical circle just fast enough to prevent the string from going slack at the top of the circle. The speed of the ball at the bottom of the circle is: Page 7 26. A small object of mass m starts at rest at the position shown and slides along the frictionless loop-the-loop track of radius R. What is the smallest value of y such that the object will slide without losing contact with the track? A) R/4 B) RQ C) R D) 2R E) zero 27. The diagram shows a plot of the potential energy as a function of x for a particle moving along the x axis. The points of unstable equilibrium are: A) only a B) only b C) only 0 D) only C! E) b and d Page 8 28. Three identical blocks move either on a horizontal surface, up a plane, or down a plane, as shown below. They all start with the same speed and continue to move until brought to rest by friction. Rank the three situations according to the mechanical energy dissipated by friction, least to greatest. _;. V 1? g' 7* 5' I f (3) (1) {2) A) The same for all cases B) 1,2,3 C) 1,then2and3tie D) 3,2,] E) 2,1,3 Page 9 Answer Key ._. PP?”H9‘E*":“P’E"E‘ I—In—Oh—l DJINJh-I NMNMMMNn—tr—nb—nr—Ir—In—I 9‘3”???)7‘950W‘Hg‘y'? m 2‘4 28. E Page I0 ...
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