Physics 201, Midterm Exam 1, Fall Answer Key

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1 Physics 201, Midterm Exam 1, Fall 2006 Answer Key 1) The equation for the change of position of a train starting at x = 0 m is given by x(t) = 1 2 at 2 + bt 3. The dimensions of b are: A. T 3 B. LT 3 C. LT 2 D. LT 1 E. L 1 T 1 2) For the x(t) given in the previous problem, given a and b are positive, the train s: A. acceleration is zero B. acceleration is constant but non zero C. acceleration decreases with time D. acceleration increases with time E. acceleration changes non-monotonically with time 3) The velocity at the midway point of a ball able to reach a height y when thrown with vertical velocity v 0 at the origin is: A. v 0 2 B. v 0 2 2gy C. v D. v gy E. gy

4) A particle moving along the x-axis has a position given by x = 54t! 2.0t 3 m. At the timet = 3.0 s, the speed of the particle is zero. Which statement is correct? A. The particle remains at rest aftert = 3.

5) Two identical balls are at rest and side by side at the top of a hill. You let one ball, A, start rolling down the hill.

2 4) A particle moving along the x-axis has a position given by x = 54t! 2.0t 3 m. At the timet = 3.0 s, the speed of the particle is zero. Which statement is correct? A. The particle remains at rest aftert = 3.0 s. B. The particle no longer accelerates after t = 3.0 s. C. The particle can be found at positions x < 0 m only whent < 0 s. D. All of the above are correct. E. None of the above is correct. 5) Two identical balls are at rest and side by side at the top of a hill. You let one ball, A, start rolling down the hill. A little later you start the second ball, B, down the hill by giving it a shove. The second ball rolls down the hill along a line parallel to the path of the first ball and passes it. At the instant ball B passes ball A: A. it has the same position and the same velocity as A. B. it has the same position and the same acceleration as A. C. it has the same position, the same velocity and the same acceleration as A. D. it has the same velocity as A. but different acceleration. E. it has the same position as A, but different velocity and acceleration. 6) The graph below shows the velocity versus time graph for a ball. Which explanation best fits the motion of the ball as shown by the graph? A. The ball is falling, is caught and is thrown down with greater velocity. B. The ball is rolling, stops and then continues rolling. C. The ball is rising, hits the ceiling, and falls down. D. The ball is falling, hits the floor, and bounces up. E. The ball is rising, is caught, and is thrown down.

7) A juggler throws two balls to the same height so that one is at the halfway point going up when the other is at the halfway point coming down. At that point: A.

3 7) A juggler throws two balls to the same height so that one is at the halfway point going up when the other is at the halfway point coming down. At that point: A. Their velocities and accelerations are equal. B. Their velocities are equal but their accelerations are equal and opposite. C. Their accelerations are equal but their velocities are equal and opposite. D. Their velocities and accelerations are both equal and opposite. E. Their velocities are equal to their accelerations. 8) A skier leaves a ski jump with a horizontal velocity of 29.4 m/s. The instant before she lands three seconds later, her speed is: A. zero B m/s C m/s D m/s E m/s 9) A toy rocket, launched from the ground, rises vertically with an acceleration of 20 m/s 2 for 6.0 s, when its motor stops. Disregarding any air resistance, what maximum height above the ground will the rocket achieve? A. 1.1 km B km C. 1.9 km D km E. 1.5 km

4 10) Vectors A and B have equal non-zero magnitudes. Which statement is always true? A. A B = 0. B. A B is perpendicular to A + B. C. B A is perpendicular to A B. D. A B is parallel to A + B. E. The magnitude of A B equals the magnitude of A + B. 11) A stunt pilot performs a circular dive of radius 800 m. At the bottom of the dive (point B in the figure) the pilot has a speed of 200 m/s, which at that instant is increasing at a rate of 20 m/s 2. What acceleration does the pilot have at point B? A. (50i + 20j) m/s 2 B. (20i 50j) m/s 2 C. (20i + 50j) m/s 2 D. ( 20i + 50j) m/s 2 E. (-50i + 20j) m/s 2 12) The speed of a particle moving in a circle 2.0 m in radius increases at the constant rate of 4.4 m/s 2. At an instant when the magnitude of the total acceleration is 6.0 m/s 2, what is the speed of the particle? A. 3.9 m/s B. 2.9 m/s C. 3.5 m/s D. 3.0 m/s E. 1.4 m/s

13) A tennis player wants to slam a serve from the point O so that the ball lands just inside the opposite corner of the court. What should the ratio v 0 y v 0 x be for the initial velocity v 0?

Car A travels at a constant speed of 20 m/s. Car B starts at rest and speeds up with constant tangential acceleration until its speed is 40 m/s.

5 13) A tennis player wants to slam a serve from the point O so that the ball lands just inside the opposite corner of the court. What should the ratio v 0 y v 0 x be for the initial velocity v 0? The time t = 0 is the time when the ball is hit by the racket. A. W L B. L W C. 1 2 gt 2 L D. 1 2 gt 2 W E. 1 2 gt 2 L 2 + W 2 14) Two cars are traveling around identical circular racetracks. Car A travels at a constant speed of 20 m/s. Car B starts at rest and speeds up with constant tangential acceleration until its speed is 40 m/s. When car B has the same (tangential) velocity as car A, it is always true that: A. It is passing car A. B. It has the same linear (tangential) acceleration as car A. C. It has the same centripetal acceleration as car A. D. It has the same total acceleration as car A. E. It has traveled farther than car A since starting. 15) A student in the front of a school bus tosses a ball to another student in the back of the bus while the bus is moving forward at constant velocity. The speed of the ball as seen by a stationary observer in the street: A. Is less than that observed inside the bus. B. Is the same as that observed inside the bus. C. Is greater than that observed inside the bus. D. May be either greater or smaller than that observed inside the bus. E. May be greater, smaller, or equal to that observed inside the bus.

16) Two balls, projected at different times so they don t collide, have trajectories A and B, as shown below. Which statement is correct? A. Their speeds v 0B must be greater than v 0A. B. Ball A is in the air for a longer time than ball B.

17) A bullet is fired vertically down from the top of a building. If it travels a distance D in time t, then how far will it have traveled in 2t? A. 1.414 D B. 2 D C. 4 D D. 9 D E.

6 16) Two balls, projected at different times so they don t collide, have trajectories A and B, as shown below. Which statement is correct? A. Their speeds v 0B must be greater than v 0A. B. Ball A is in the air for a longer time than ball B. C. Ball B is in the air for a longer time than ball A. D. Ball B has a greater acceleration than ball A. E. Ball A has a greater acceleration than ball B. 17) A bullet is fired vertically down from the top of a building. If it travels a distance D in time t, then how far will it have traveled in 2t? A D B. 2 D C. 4 D D. 9 D E. None of the above 18) A baseball is hit at ground level. The ball is observed to reach its maximum height above ground level 3.0 s after being hit. And 2.5 s after reaching this maximum height, the ball is observed to barely clear a fence that is 97.5 m from where it was hit. How high is the fence? A. 8.2 m B m C m D m E. 4.9 m

7 19) A projectile is thrown from the top of a building with an initial velocity of 30 m/s in the horizontal direction. If the top of the building is 30 m above the ground, how fast will the projectile be moving just before it strikes the ground? A. 0 m/s B. Less than 30 m/s C. 30 m/s D. Between 30 m/s and 50 m/s E. Greater than 50 m/s 20) A tennis ball, a baseball and a basketball are dropped from a hot air balloon at the same time, when it is 300 m above ground. Which of the following statements is true about the speeds of the balls after the tennis ball has traveled 30 m? (Ignore air resistance) A. V tennis = V baseball = V basketball B. V tennis > V baseball > V basketball C. V tennis < V baseball < V basketball D. Answer depends on the unknown distances traveled by the other balls E. Answer depends on the unknown masses of the balls

Chapter 2 Motion in One Dimension

Chapter 2 Motion in One Dimension Multiple Choice 1. The position of a particle moving along the x axis is given by 2 x = ( 21+ 22t 6 0. t )m, where t is in s. What is the average velocity during the time