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CU-Boulder PHYS 1110 - Questions

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CT4-1. A bullet is fired horizontally from a rifle on the Moon (where there is no air). The initial speed of the bullet when it leaves the gun barrel is vo. Assume that the ground is perfectly level (and endless). Which one, if any, of the following three statements is false:A: During its entire flight, the minimum speed of the bullet is vo.B: The acceleration of the bullet is constant during its flight.C: The time it takes for the bullet to hit the ground increases as vo is increased.ORD: All of the above statements are true!Answer: Statement C is false. The time for the bullet to hit the ground is independent of the muzzle velocity. The bullet hits the ground in the same time it would if it just dropped straight down from the end of the barrel.Regarding answer A, the minimum speed of the bullet is vo, the speed it has when it first leaves the gun. The total speed is  22o2y2xgtvvvv , which grows with time t. CT3-2. Two projectiles are fired from a cannon. For projectile A, the cannon is tilted upward at an angle twice that of projectile B. (As usual, neglect air resistance.)Which projectile was in the air longer?A B ABC: A and B were in the air the same length of time.D: Not enough information to answer the question.Answer: Projectile A is in flight longer. . The y-motion is independent of the x-motion. The flight times are controlled solely by the y motion. Projectile A has a larger y-component of initial velocity, v0y = v0sin, so it is in flight longer.CT4-3. A rifle is accurately aimed at a rabid monkey hanging from the branch of a tree. The instant the gun is fired, the monkey releases the branch and starts falling. The monkey is well within the range of the rifle. The initial speed of the bullet is vo. What happens?A: The bullet finds its target, regardless of the value of vo. (Assuming vo still large enough to reach the air below the monkey.)B: The bullet hits the monkey only if vo is large enough.C: The bullet misses.Answer: The bullets hits the monkey always, just so long as vo is large enough to reach the air space below the monkey. See lecture notes 4-4, 4-5.CT4-4. A hunter shoots a monkey in intergalactic space (where there is no gravity). The bullet flies in a straight line and hits the monkey. The path of the bullet is described by the vector equationtvrroo vogunWhen the time t is such that the bullet is half-way to the monkey, the vector ris which vector on the diagram? Answer: Vector C is r. Vector A is or. Vector B is tvo.CT4-5A particle is moving along the path shown, with constant speed. Its velocity vector at two different times is shown. What is the direction of the acceleration when the particle is at point X?xyPath of bulletstartfinishxyBACAnswer: To the left. The direction of the acceleration is toward the center of the circle .Recall that 2 1dv v v vadt t t    r r uur uurr.XDCBA(E) None of thesev1 v2 vCT4-6A race car travels around the track shown at constant speed. Over which portion of the track is the magnitude of the acceleration the smallest?A) From 1 to 2 B) From 3 to 4C) Neither of these D) Both of theseAnswer: It’s a dirty trick! The answer is neither of these. The acceleration is a minimum from 2 to 3, and from 4 to 1, where a = 0 (constant


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