Practice Test What two units of measurement are necessary for describing speed?

Transcription

1 Practice Test 1 1. What two units of measurement are necessary for describing speed? 2. What kind of speed is registered by an automobile? 3. What is the average speed in kilometers per hour for a horse that gallops a distance of 15 km in a of 30 min? 4. How far does a horse travel if it gallops at an average speed of 25 km/hr for 30 min.? 5. Distinguish between speed and velocity. 6. If a car moves with constant velocity, does it also move with constant speed? 7. If a car is moving at 90 km/hr and it rounds a corner, also at 90 km/hr, does it maintain a constant speed? A constant velocity? 8. Distinguish between velocity and acceleration. 9. What is the acceleration of a car that increases its velocity from 0 to 100 km/hr in 10 seconds? 10. What is the acceleration of a car that maintains a constant velocity of 100 km/hr for 15 seconds? 11. When are you most aware of motion in a moving vehicle? 12. What is meant by a freely falling body? 13. What is the gain in speed per second for a freely falling object? 14. What is the velocity of an object, 5 seconds after it is dropped? 6 seconds? 15. What relationship between distance traveled and did Galileo discover for accelerating objects? 16. What is the distance traveled for a free falling object that starts from rest, 5 sec and 6 sec after it is released? 17. What is the effect of air resistance on falling objects? 18. Consider these measurements: 10 m, 10 m/s, 10 m/s 2 Which one is velocity, which one is acceleration and which one is speed?

2 19. What is the impact speed when a car moving at 100 km/hr bumps into the rear of another car traveling in the same direction at 98 km/hr? 20. John can paddle a canoe in still water at 8 km/hr. How fast will he be moving forward at canoeing upstream in a river that flows at 8 km/hr? 21. Is a ticket fine for speeding based on one s average speed or instantaneous speed? 22. One airplane travels due north at 300 km/hr while another travels due south a 300 km/hr. Are their speeds the same? Are their velocities the same? Explain. 23. Light travels at 3x10 8 m/s. What is the acceleration of light? 24. Can an automobile with a velocity toward the north, have an acceleration toward the south? 25. A ball thrown straight up will rise and then reverse its direction and fall. Draw the acceleration vector of the ball. 26. You are driving north on the highway. Then, without changing speed, you round a curve and drive east. (a) Does your velocity change? (b) Do you accelerate? Explain. 27. You round a corner in your car at 60 km/hr. Do you have a constant velocity? Do you have any acceleration? 28. Starting from rest, one car accelerates to a speed of 50 km/h, and another car accelerates to a speed of 60 km/h. Can you say which car underwent the greater acceleration? 29. Can an object be moving when its acceleration is zero? 30. Can you give an example wherein the acceleration of a body is opposite in direction to its velocity? 31. What is the acceleration of a car that moves at a steady velocity of 100 km/hr for 100 seconds? Explain you answer. 32. Suppose that a freely falling object were somehow equipped with a speedometer. By how much would its speed reading increase with each second of fall? 33. Suppose that the freely falling object in the preceding exercise were also equipped with an odometer. Would the readings of distance fallen each second indicate equal or different falling distances for successive seconds? Explain.

3 34. Disregarding air friction, For a freely falling object dropped from rest, what is its acceleration at the end of the 5th second of fall? The 10th? Defend your answer. 35. If air resistance can be neglected, how does the acceleration of a ball that has been tossed straight upward compare with its acceleration if simply dropped? 36. Disregarding air friction, when a ball player throws a ball straight up, by how much does the speed of the ball decrease each second while ascending? By how much does it increase each second while descending? How much is required for rising compared to falling? 37. Someone standing at the edge of a cliff throws a ball straight up at a certain speed and another ball straight down with the same initial speed. If air resistance is negligible, which ball will have the greater speed when it strikes the ground below? Explain. 38. Disregarding air friction, if you drop an object, its acceleration toward the ground is 9.8 m/s/s. If you throw it down instead, would its acceleration after throwing be greater than 9.8 m/s/s? Why or why not? 39. Consider a vertically-launched projectile when air drag is negligible. When is the acceleration due to gravity greater: when ascending, at the top, or when descending? Defend you answer. 40. If it were not for air friction, why would it be dangerous to go outdoors on rainy days? 41. Find the velocity of a tennis ball after 8 second when it is dropped from rest assuming there is no air resistance. 42. Find the displacement of the tennis ball after 8 seconds when it is dropped from rest assuming there is no air resistance. 43. A climber near the summit of a vertical cliff accidentally knocks loose a large rock. She sees it shatter at the bottom of the cliff 8 seconds latter. a) What was the speed of the rock when it hit the ground? b) How far did the rock fall? 44. If you throw a rock off a cliff, how do the horizontal components of its velocity compare for all points along its trajectory? 45. A basketball is thrown up as a projectile when there is no air friction. Draw the horizontal and vertical components of its horizontal and vertical velocity.

4 46. A car increases its velocity from zero to 60 km/hr in 10 seconds. Its acceleration is a) 50 km/hr/sec b) 70 km/hr/sec c) 1 / 6 km/hr/sec d) 6 km/hr/sec e) 6 m/s When a body is in free fall (no air resistance) a. Its acceleration increases b. Its speed increases c. Both a and b are true d. Neither a nor b are true 48. Projectile motion is a combination of a. constant vertical velocity and constant horizontal acceleration b. constant horizontal velocity and constant vertical acceleration c. constant vertical velocity and constant horizontal velocity d. constant vertical acceleration and constant horizontal acceleration e. constant vertical acceleration and constant horizontal velocity Sketch the following graphs: 49. You start at the origin. You walk quickly and steadily away from the origin, stop for a moment, and then walk slowly and steadily back to your starting point. 50. You drop a ball from a height of three meters above the ground. (Call upward the positive direction). Sketch the following plots. Vertical Velocity Acceleration

5 51. After you give a cart an initial push toward the detector, it slows down, turns around, and then speeds up again toward its initial position (t = 0 is right after you end your push). The motion detector is the origin and away from the detector is the positive direction. Initial Motion Detector Gentle Push a. Draw the motion diagram of the cart moving to the left and to the right. b. Draw the graphs describing the motion of the cart from the moment after it leaves your hand. Velocity Acceleration 52. Describe in words the motion being described by the graph below (that is, fill in the table with the options provided in italics below): (It may be useful to keep in mind the x v definitions for velocity and acceleration: v = Δ Δ ; a = ) Δt Δt D E B C F G A

6 As the object goes from The object is (moving away from the detector, toward the detector. Standing still) The object s velocity is (positive, negative, zero) Object is (Moving at a constant speed, speeding up, slowing down, at rest) The object s acceleration is (positive, negative, zero) A to B B to C C to D D to E E to F F to G In Each of the following graphs, which line (A or B) represents the greater speed? Explain. 53. A B Line represents the greater speed. I can tell this because: 54. Velocity A B Line represents the greater speed. I can tell this because: 55. A B Line represents the greater speed. I can tell this because:

7 In all of the problems below, assume that air resistance can be neglected. In questions requiring calculations, show the formula you are starting with (it should be one on the formula page), show the formula rearranged, show the numbers (with units) substituted into the formula, and show the answer (with units). Put a box around your answer. 56. A ball is dropped from rest from a tower and strikes the ground 38 m below. How many seconds does it take for the ball to strike the ground after being dropped? 57. A body initially at rest is accelerated at a constant rate for 8 seconds in the positive direction. If the final speed is 20 m/s, what is the acceleration? 58. Determine the distance traveled by the object whose motion is illustrated by the graph: 6 m/s Velocity 8 s 13 s 59. Suppose you toss a basketball straight up, and measured its position, velocity, and acceleration using a motion sensor. Take t =0 to be the at which the ball leaves your hands, and the final to be the moment right before you start to catch the ball. Take upward to be the positive direction. Draw appropriate graphs below for the motion of the basketball: Velocity (m/s) Motion Detector Acceleration (m/s 2 ) (m)

8 60. Explain the sign of the acceleration on the way up, at the maximum height, and on the way down. In lab you analyzed a basketball shot. 61. Sketch below the velocity graphs that you got for the basketball shot, starting from immediately after the ball left the shooter s hands until right before it hit the ground the first. v y v x 62. Sketch below the acceleration graphs that you would have gotten for the basketball shot. a y a x

9 We did an experiment where we dropped a ball and simultaneously launched another ball horizontally: 63. We dropped (and launched) the balls from a height of 1.4 m above the ground. If the launched ball landed 2.6 meters away horizontally from its initial position (as shown on the diagram), determine the ball s initial horizontal speed. 1.4 m A B 2.6 m 64. Suppose you have an airplane whizzing around in a circle. Here is the top view of that plane: Draw vectors indicating the velocity and acceleration of the airplane. 65. If the plane is travelling at 40 m/s and the radius of the circle is 1.0 km. What is the acceleration of the plane? 66. Here s a top view of a second plane also whizzing around in a circle. Draw vectors indicating the velocity and acceleration of this airplane.

10 67. In a short amount of, a plane moves a short distance around a circle as shown below. Give a good explanation of why the change in velocity of the plane is toward the center.