Wilson, College Physics, 6th Edition
Chapter 2
Exercises
MC = Multiple Choice Question, CQ = Conceptual Question and IE = Integrated Exercise. Throughout the text, many exercise sections will include “paired” exercises. These exercise pairs, identified with red numbers, are intended to assist you in problem solving and learning. In a pair, the first exercise (even numbered) is worked out in the Study Guide so that you can consult it should you need assistance in solving it. The second exercise (odd numbered) is similar in nature, and its answer is given at the back of the book.
2.1 Distance and Speed: Scalar Quantities and
2.2 One-Dimensional Displacement and Velocity: Vector Quantities
1. MC A scalar quantity has (a) only magnitude, (b) only direction, (c) both magnitude and direction.(a)
2. MC What can be said about distance traveled relative to the magnitude of displacement? (a) greater than, (b) equal to, (c) both a and b.(c)
3. MC A vector quantity has (a) only magnitude, (b) only direction, (c) both direction and magnitude.(c)
4. MC What can be said about average speed relative to the magnitude of the average velocity? (a) greater than, (b) equal to, (c) both a and b.(c)
5. CQ Can the displacement of a person’s trip be zero, yet the distance involved in the trip be nonzero? How about the reverse situation? Explain.see ISM
6. CQ You are told that a person has walked 750 m. What can you safely say about the person’s final position relative to the starting point?no final position can be given; may be 0 to 750 m from start
7. CQ If the displacement of an object is 300 m north, what can you say about the distance traveled by the object?the distance traveled is greater than or equal to 300 m
8. CQ Speed is the magnitude of velocity. Is average speed the magnitude of average velocity? Explain.no, see ISM
9. CQ The average velocity of a jogger on a straight track is computed to be Is it possible for the jogger’s instantaneous velocity to be negative at any time during the jog? Explain.yes, see ISM
10. l What is the magnitude of the displacement of a car that travels half a lap along a circle that has a radius of 150 m? How about when the car travels a full lap?300 m; zero
11. l A student throws a rock straight upward at shoulder level, which is 1.65 m above the ground. What is the displacement of the rock when it hits the ground?1.65 m down
12. l In 1999, the Moroccan runner Hicham El Guerrouj ran the 1-mi race in 3 min, 43.13 s. What was his average speed during the race in
13. l A senior citizen walks 0.30 km in 10 min, going around a shopping mall. (a) What is her average speed in meters per second? (b) If she wants to increase her average speed by 20% in walking a second lap, what would her travel time in minutes have to be?(a) (b) 8.3 min
14. ll A hospital patient is given 500 cc of saline by IV. If the saline is received at a rate of how long will it take for the half liter to run out?125 min
15. ll A hospital nurse walks 25 m to a patient’s room at the end of the hall in 0.50 min. She talks with the patient for 4.0 min, and then walks back to the nursing station at the same rate she came. What was the nurse’s average speed?
16. ll On a cross-country trip, a couple drives 500 mi in 10 h on the first day, 380 mi in 8.0 h on the second day, and 600 mi in 15 h on the third day. What was the average speed for the whole trip?
17. IE ll A car travels three quarters of a lap on a circular track of radius R. (a) The magnitude of the displacement is (1) less than R, (2) greater than R, but less than (3) greater than (b) If what is the magnitude of the displacement?(a) (2) greater than R, but less than (b) 71 m
18. IE ll A race car travels a complete lap on a circular track of radius 500 m in 50 s. (a) The average velocity of the race car is (1) zero, (2) (3) (4) none of the preceding. Why? (b) What is the average speed of the race car?(a) (1) zero (b)
19. IE ll A student runs 30 m east, 40 m north, and 50 m west. (a) The magnitude of the student’s net displacement is (1) between 0 and 20 m, (2) between 20 m and 40 m, (3) between 40 m and 60 m. (b) What is his net displacement?(a) (3) between 40 m and 60 m (b) 45 m at 27° west of north
20. ll A student throws a ball vertically upward such that it travels 7.1 m to its maximum height. If the ball is caught at the initial height 2.4 s after being thrown, (a) what is the ball’s average speed, and (b) what is its average velocity?(a) (b) zero, displacement is zero
21. ll An insect crawls along the edge of a rectangular swimming pool of length 27 m and width 21 m (6Fig. 2.17). If it crawls from corner A to corner B in 30 min, (a) what is its average speed, and (b) what is the magnitude of its average velocity?(a) (b)
22. ll Consider motion on the Earth’s surface during one complete day. (a) What is the average velocity of a person on the Earth’s equator? (b) What is the average speed of a person on the Earth’s equator? (c) Compare these two results to a person located exactly at the Earth’s North Pole.(a) zero (b) (c) both zero
23. ll A high school kicker makes a 30.0-yd field goal attempt (in American football) and hits the crossbar at a height of 10.0 ft. (a) What is the net displacement of the football from the time it leaves the ground until it hits the crossbar? (b) Assuming the football took 2.5 s to hit the crossbar, what was its average velocity? (c) Explain why you cannot determine its average speed from this data.(a) (b) (c) see ISM
24. ll A plot of position versus time is shown in 4Fig. 2.18 for an object in linear motion. (a) What are the average velocities for the segments AB, BC, CD, DE, EF, FG, and BG? (b) State whether the motion is uniform or nonuniform in each case. (c) What is the instantaneous velocity at point D?see ISM
25. ll In demonstrating a dance step, a person moves in one dimension, as shown in 6Fig. 2.19. What are (a) the average speed and (b) the average velocity for each phase of the motion? (c) What are the instantaneous velocities at 2.5 s, 4.5 s, and 6.0 s? (d) What is the average velocity for the interval between and [Hint: Recall that the overall displacement is the displacement between the starting point and the ending point.]see ISM
26. ll You can determine the speed of a car by measuring the time it takes to travel between mile markers on a highway. (a) How many seconds should elapse between two consecutive mile markers if the car’s average speed is (b) What is the car’s average speed if it takes 65 s to travel between the mile markers?(a) 51 s (b)
27. ll Short hair grows at a rate of about A college student has his hair cut to a length of 1.5 cm. He will have it cut again when the length is 3.5 cm. How long will it be until his next trip to the barber shop?1 month
28. lll A student driving home for the holidays starts at 8:00 am to make the 675-km trip, practically all of which is on nonurban interstate highway. If she wants to arrive home no later than 3:00 pm, what must be her minimum average speed? Will she have to exceed the speed limit? no
29. lll A regional airline flight consists of two legs with an intermediate stop. The airplane flies 400 km due north from airport A to airport B. From there, it flies 300 km due east to its final destination at airport C. (a) What is the plane’s displacement from its starting point? (b) If the first leg takes 45 min and the second leg 30 min, what is the average velocity for the trip? (c) What is the average speed for the trip? (d) Why is the average speed not the same as the magnitude for the average velocity?see ISM
30. lll Two runners approaching each other on a straight track have constant speeds of and respectively, when they are 100 m apart (6Fig. 2.20). How long will it take for the runners to meet, and at what position will they meet if they maintain these speeds?12.5 s, 56.3 m (relative to runner on left)
2.3 Acceleration
31. MC On a position-versus-time plot for an object that has a constant acceleration, the graph is (a) a horizontal line, (b) a nonhorizontal and nonvertical straight line, (c) a vertical line, (d) a curve.(d)
32. MC An acceleration may result from (a) an increase in speed, (b) a decrease in speed, (c) a change of direction, (d) all of the preceding.(d)
33. MC A negative acceleration can cause (a) an increase in speed, (b) a decrease in speed, (c) either a or b.(c)
34. MC The gas pedal of an automobile is commonly referred to as the accelerator. Which of the following might also be called an accelerator: (a) the brakes; (b) the steering wheel; (c) the gear shift; or (d) all of the preceding? Explain.(d)
35. CQ A car is traveling at a constant speed of on a circular track. Is the car accelerating? Explain.yes, see ISM
36. CQ Does a fast-moving object always have higher acceleration than a slower object? Give a few examples, and explain.not necessarily, see ISM
37. CQ A classmate states that a negative acceleration always means that a moving object is decelerating. Is this statement true? Explain.not necessarily, see ISM
38. CQ Describe the motions of the two objects that have the velocity-versus-time plots shown in 6Fig. 2.21.See ISM
39. CQ An object traveling at a constant velocity experiences a constant acceleration in the same direction for a period of time t. Then an acceleration of equal magnitude is experienced in the opposite direction of for the same period of time t. What is the object’s final velocity?
40. l An automobile traveling at along a straight, level road accelerates to in 6.00 s. What is the magnitude of the auto’s average acceleration?
41. l A sports car can accelerate from 0 to in 3.9 s. What is the magnitude of the average acceleration of the car in meters per second squared?
42. l If the sports car in Exercise 41 can accelerate at a rate of how long does the car take to accelerate from 0 to 3.7 s
43. IE ll A couple is traveling by car down a straight highway. They see an accident in the distance, so the driver applies the brakes, and in 5.0 s the car slows down uniformly to rest. (a) The direction of the acceleration vector is (1) in the same direction as, (2) opposite to, (3) at 90° relative to the velocity vector. Why? (b) By how much must the velocity change each second from the start of braking to the car’s complete stop?(a) (2) opposite to velocity (b) each second, opposite direction of velocity
44. ll A paramedic drives an ambulance at a constant speed of on a straight street for ten city blocks. Because of heavy traffic, the driver slows to in 6.0 s and travels two more blocks. What was the average acceleration of the vehicle?
45. ll With good tires and brakes, a car traveling on dry pavement can travel 400 ft when the driver reacts to something he sees and brings the vehicle to a stop. If this is done uniformly, what is the car’s acceleration? (These are actual conditions and 400 ft is about the length of a city block.)
46. ll A ball is thrown straight up at an initial speed of and, on returning to your hand, hits it moving downward at that same speed. If the whole trip took 2.0 s, determine the ball’s (a) average acceleration and (b) average velocity.(a) (b) 0
47. ll After landing, a jetliner on a straight runway taxis to a stop at an average velocity of If the plane takes 7.00 s to come to rest, what are the plane’s initial velocity and acceleration? or
48. ll A train on a straight, level track has an initial speed of A uniform acceleration of is applied while the train travels 200 m. (a) What is the speed of the train at the end of this distance? (b) How long did it take for the train to travel the 200 m?(a) (b) 11.1 s