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1 Vectors Q and R have the same magnitude. If vector Q is in the +x direction and vector R is in the –y direction, what is the direction of vector T = Q – R?Answer: upper right 2 You know the acceleration of a particle at all times. What do you know about the direction of the velocity of the particle?A: You know nothing about the direction of the velocity.B: You know that the direction of the velocity is either parallel to, anti-parallel to, or at right angles to the direction of the acceleration.Answer: You know nothing about the direction of the velocity. Knowing the direction of the rateof change of velocity (the acceleration) tells you nothing at all about the direction of the velocity.Velocity is not acceleration; acceleration is not velocity.A BC DE) None of these3A simple pendulum is swinging back and forth. What is the direction of the acceleration of the pendulum mass at the moment when it is at maximum displacement to the right?A: zeroE) None of theseAnswer: Yellow. Lower left. The acceleration is in the same direction as 2 1v v v  r r r, where v1 is the velocity just before the mass stops and v2 is the velocity just after it stops.A free-body diagram of the forces on the ball when it is at the extreme rightposition is shown.Suppose now the ball swings back and forth betweenhorizontal positions:When the ball is in the horizontal position, the tension in the string is A: zeroB: not zero.BCDmg T Fnet v1 v2 vAnswer: The tension is zero. By the same 2 1v v v  r r r argument as in the question above, one can show that the acceleration is straight down when the mass on the extreme right with the string horizontal. Since the acceleration is straight down, the net force must be straight down, so there can be no horizontal component to the net force, so the tension must be zero. Alternatively, one can say that the radial part of the acceleration is ar = v2/r, and since v = 0 instantaneously, ar must be zero, so there must be no force along the radial direction.4A computer monitor is thrown upward. It rises to a height h and falls back down to Earth. During the flight, the work done by the force of gravity is...A: mgh B: 2mgh C: zero D: -mgh E: -2mghAnswer: Work done by gravity is zero. (Work is negative on the way up, positive on the way down.)During the flight, the work done by the drag force of air resistance is..A: zero B: positive C: negativeAnswer: Negative. The drag force is always in the direction opposite the displacement, so the work done is always negative, both on the way up and on the way down.h5 A Cadillac and a Volkswagen have a head-on collision and stick to together in a mangled pile of metal. The police determine that the wreckage is in the exact same spot where the two cars collided. Detective O'Newton (who got an A in Physics 2010) writes in his report that, just prior to the collision, the two cars had the same... A: magnitude of momentum. B: kinetic energy.C: mass. D: speed.Answer: MomentumWhich car had the larger speed?A: Cadillac B: VolkswagenAnswer: Volkswagen6 Schwinn decides to redesign its model X-2000 28-speed "Road Warrior" bike ($129.95). The rims of the wheels are made lighter but more weight is added to the frame so the total weight of the bike remainsunchanged.Compared to the old bike, when the new bike is moving at a given speed, its total kinetic energy is..A: less. B: greater C: the same.Answer: less (same translation KE, but smaller rotational KE in the wheels)Compared to the old bike, when the new bike is accelerated from rest up to a given speed, does the rider have to work less, more, or the same?A: less. B: greater C: the same.Answer: less. Work done by rider went into increasing the KE. KEtot = KEtrans+KErot. In the two cases, we have the same KEtrans = (1/2)Mv2, but the KErot of the wheels is less with the new bike.7 A distraught student standing at the edgeof a cliff throws one calculator straight upand another calculator straight down at thesame initial speed. Neglecting airresistance, the one which hits the groundwith the greatest speed is the one thrown ... A: upward. B: downward.C: neither–they both hit at the same speed.Answer: They both hit at the same speed.Same question, but now do not neglect air resistance. The calculator which hits with the greatest speed is the one thrown..A: upward. B: downward.C: neither–they both hit at the same speed.Answer: downward8 A flaming physics text is dropped froman airplane flying at height h at constanthorizontal velocity and speed vo. Neglecting air resistance, the text will...A: quickly lag behind the planeB: remain vertically under the planeC: move ahead of the planeD: it depends how fast the plane is flying.Answer: text remains under the plane. vx = vo = constant.What is the speed with which the text hits the ground?A: 0v 2g hB: 0v 2g hC: Neither[Hint: For 1D motion along Y: v2 = v02 + 2ay (y-y0).]Answer: Neither. Correct answer is 2 2 2x y 0speed v v v 2g h   .h vo9 Consider an exhausted physics student standing in an elevator that is moving upward with constant velocity. The upward normal force N exerted by the elevator floor on the student isA: larger than B: identical to C: smaller thanthe weight mg of the person.Answer: identical. The net force is zero, since the velocity is constant.10 A student attempting to make her 9th pot of coffee isso shaky she drops the coffee filter. The coffee filterfloats gently downward, at some constant ("terminal")velocity v.The net force on the coffee filter isA: UpwardsB: DownwardsC: Zero.Answer: Zero. Since the velocity is constant.v=constant11 A relieved physics student driving away from CU on Dec. 15 wishes to cause her car to accelerate. How many controls in an ordinary car are specifically designed and intended to accelerate the vehicle?A: one B: two C: threeD: more than threeAnswer: I can think of three: The accelerator pedal, the brake, and the steering wheel. Possibly, also the clutch. ( Some people use the clutch to slow the car.)12 At some instant in time, twoasteroids in deep space are a distancer = 20 km apart. Asteroid 2 has 10 timesthe mass of asteroid 1. What is the ratioof their resulting acceleration (due to thegravitational attraction between them)?a1 / a2 = A: 10 B: 1/10 C: 1D: None of these/don't knowAnswer: 10This is a problem with constant acceleration, so we can use the constant acceleration formulas.A: True B: FalseFalse: As they get closer, the


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CU-Boulder PHYS 2010 - Questions

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