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CU-Boulder PHYS 1110 - PHYS 1110 Review Questions

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1 of 12 10/17/2011 ReviewII-1. Consider the vectors V1 and V2 shown. What is the direction of V = V2 – V1 , V1 + V = V2 Answer: B, downward ReviewII-2. Consider the vector A Which equation is correct? A) Ax = +A cos B) Ax = –A cos C) Ax = +A sin D) Ax = –A sin Answer: Ax = –A sin ReviewII-3. A mass m is lowered on a string. The mass is moving downward but it is slowing down. How does the magnitude of the tension T in the string compare to the magnitude of the net force, Fnet , on the mass ? A) Fnet = T B) Fnet >T C) Fnet < T D) Impossible to tell from the information given. Answer: Draw the FBD: Fnet < T v1 v2 direction of v? A B C D A x y m moving downward, and slowing2 of 12 10/17/2011 ReviewII-4. The graph shows velocity vs. time for a train moving along a straight track. The graph shows that the train is … A) speeding up all the time. B) slowing down all the time. C) speeding up initially, but then slows down. D) slowing down initially, but then speeds up. E) changing direction. Answer: speeding up all the time. (Note the plot is v vs. t, NOT x vs. t ) ReviewII-5. The free-body diagram for a car rounding a banked curve is shown. The car is going so fast that it is about to slip. The coordinate system has been chosen as shown. What is the correct y-equation? A) N sin + sN cos – mg = 0 B) N – sN sin – mg cos = 0 C) N – mg cos = 0 D) N cos – sN sin – mg = 0 E) None of these Answer: N cos – sN sin – mg = 0 a SN N mg x y t v3 of 12 10/17/2011 ReviewII-6. A crate of mass m is accelerated to the left with a string at an angle q above the horizontal. The coefficient of kinetic friction is K. The coordinate system has been chosen as shown. What is the correct x–equation? A) F N mg 0   B) KFcos N ma   C) Fsin N mg 0    D) kFcos N mg N ma     E) None of these Answer: KFcos N ma   ReviewII-7. A block of mass m on a table is pulled along a table by an external horizontal force of magnitude Fext , as shown. The table has a rough surface so there is a frictional force of magnitude Ffric on block. The block is moving at constant speed v. How do the magnitudes of the external force Fext and the friction force Ffric compare? A) Fext = Ffric B) Fext > Ffric C) Fext < Ffric Answer: Fext = Ffric F a Kx Fext v = constant4 of 12 10/17/2011 ReviewII-8. Consider the following two situations: Situation I: A car on Earth rides over the top of a round hill, with radius of curvature = 100 m, at constant speed v = 35 mph. Situation II: A monorail car in intergalactic space (no gravity) moves along a round monorail, with radius of curvature = 100 m, at constant speed v = 35 mph. Which car experiences larger acceleration? A) Earth car B) Space car C) Both cars have the same acceleration. Answer: Both cars have the same acceleration. The presence of gravity doesn’t change the fact that the acceleration has magnitude a = v2/r. II I5 of 12 10/17/2011 ReviewII-9. A rider in a "barrel of fun" finds herself stuck with her back to the wall. The free-body diagram is shown. Is the following statement definitely true for this situation? sN = mg A) Yes, it is certainly true. B) No, it might not be true. Answer: No, it might not be true. Only true if Ffric = sN. Static friction Ffric can have any value 0 < Ffric < sN ReviewII-10. A box of mass m is resting stationary on a board which is tilted at an angle  from the horizontal. The coefficient of static friction between the box and the board is s. The angle is rather shallow and the friction is large, so the box is not about to slip. What is the magnitude of the force of friction between the board and the box? (A) Smg (B) Smgcos (C)Smgcos (D) mgsin (E) None of these. Answer: mgsin The box is not about to slip, so the force of static friction is NOT sN6 of 12 10/17/2011 ReviewII-11. The tip of the nose of a pogo stick rider moves along the path shown. The maximum compression of the pogo stick spring is shown. At what point(A, B, C or D) is the elastic potential of the spring energy a maximum? At what point is the gravitational potential energy a maximum? At what point is the kinetic energy a maximum? Answers: PEelas is max at D, PEgrav is max at A. Of these 4 points, KE is largest at C (just before the spring starts to compress) ReviewII-12. A projectile is fired straight up and then it comes back down to its original height. There is air resistance as the projectile is moving. During the flight of the projectile, the work done by the force of gravity is.. A) zero. B) positive D) negative During the flight of the projectile, the work done by the force of air resistance is... A) zero. B) positive C) negative Answer: Wgrav = 0 (negative on the way up, positive on the way down) Wdrag = negative (drag force is always opposite the displacement) A B C D x7 of 12 10/17/2011 ReviewII-13. A pendulum is launched in two different ways. During both launches, the bob is given an initial speed of 3.0 m/s and the same initial angle from the vertical. On launch 1, the speed is upwards, on launch 2, the speed is downwards. Assume no friction. Which launch will cause the pendulum to swing the largest angle from the equilibrium position on the left side? A) Launch 1 B) Launch 2 C) Both launches give the same maximum displacement. Answer: Both launches give the same maximum displacement, if no friction 1 28 of 12 10/17/2011 ReviewII-14. A mass m is dropped from rest from a height hi above a table top on which sits a spring with spring constant k. The mass compresses the spring by a maximum amount x and stops for an instant at a height hf . There is no friction in this problem. Which of the following equations correctly expresses conservation of energy and allows one to solve for the compression x of the spring? A) mgh mv kxi 122122 B) mgh kx mghi f 122 C) mgh kx mghi f 122 D)  mg h h kx mvf i  122122 E) None of these equations is correct. Answer: mgh kx mghi f 122 ReviewII-15. A planet is in elliptical orbit around the Sun. The zero of potential energy U is chosen at …


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