# Unit 1 Review - Answers

1. If an object has an acceleration of 0 m/s2, then one can be sure that the object is not

 a. moving b. changing position c. changing velocity

2. If car A passes car B, then car A must be

1. accelerating.
2. accelerating at a greater rate than car B.
3. moving faster than car B and accelerating more than car B.
4. moving faster than car B, but not necessarily accelerating.

3. Which one of the following is NOT consistent with a car which is accelerating?

1. moving with an increasing speed.
2. moving with a decreasing speed.
3. moving with a high constant speed.
4. changing direction.

4. Barry Sanders is running down the football field in a straight line. He starts at the 0-yard line at 0 seconds. At 1 second, he is on the 10-yard line; at 2 seconds, he is on the 20-yard line; at 3 seconds, he is on the 30-yard line; and at 4 seconds, he is on the 40-yard line. This is evidence that

1. he is accelerating
2. he is covering a greater distance in each consecutive second.
3. he is moving with a constant speed (on average).

5. Barry Sanders is running down the football field in a straight line. He starts at the 0-yard line at 0 seconds. At 1 second, he is on the 10-yard line; at 2 seconds, he is on the 20-yard line; at 3 seconds, he is on the 30-yard line; and at 4 seconds, he is on the 40-yard line. What is Barry's acceleration?

6. Olympic gold medalist Michael Jackson runs one time around the track - 400 meters - in 38 seconds. What is his displacement? ___________ What is his average velocity? ___________

7. If an object is moving eastward and slowing down, then the direction of its velocity vector is

 a. eastward b. westward c. neither d. not enough info to tell

8. If an object is moving eastward and slowing down, then the direction of its acceleration vector is

 a. eastward b. westward c. neither d. not enough info to tell

9. Which one of the following quantities is NOT a vector?

 a. 10 mi/hr, east b. 10 mi/hr/sec, west c. 35 m/s, north d. 20 m/s

10. Which one of the following quantities is NOT a speed?

 a. 10 mi/hr b. 10 mi/hr/sec c. 35 m/s d. 20 m/s

11. Which one of the following statements is NOT true of a free-falling object? An object in a state of free fall

1. falls with a constant speed of -10 m/s.
2. falls with a acceleration of -10 m/s/s.
3. falls under the sole influence of gravity.
4. falls with downward acceleration which has a constant magnitude.

12. The average speed of a horse which gallops 10 kilometers (km) in 30 minutes is

 a. 10 km/hr b. 20 km/hr c. 30 km/hr d. more than 30 km/hr

13. What is the acceleration of a car that maintains a constant velocity of 100 km/hr for 10 seconds?

 a. 0 b. 10 km/hr/s c. 10 km/s/s d. 1000 km/hr/s

14. As an object freely falls, its

 a. speed increases b. acceleration increases c. both of these d. none of these

15. If a freely-falling object were somehow equipped with a speedometer, its speed reading (neglecting air resistance) would increase each second by about

 a. 5 m/s. b. 10 m/s. c. 15 m/s. d. a variable amount. e. depends on its initial speed.

16. Ten seconds after starting from rest, a freely-falling object will have a speed of about

 a. 10 m/s. b. 50 m/s. c. 100 m/s. d. more than 100 m/s.

17. As a baseball is thrown, its speed increases from 0 to 30 m/s in 0.10 seconds. The average acceleration of the baseball is

 a. 3m/s2. b. 30 m/s2. c. 300 m/s2. d. 3000 m/s2. e. none of these

18. A rocket accelerates from rest for 1 minute at 50 m/s2. The rocket's speed will be

 a. 50 m/s b. 500 m/s c. 3000 m/s d. 3600 m/s e. none of these

19. If you drop an object, it will accelerate downward at a rate of 9.8 m/s2. If you instead throw its downwards, it acceleration (in the absence of air resistance) will be

 a. less than 9.8 m/s2. b. 9.8 m/s2. c. more than 9.8 m/s2.

20. Consider drops of water that leak from a dripping faucet at a constant rate. As the drops fall they

 a. get closer together. b. get farther apart. c. remain at a relatively fixed distance from one another.

21. Renatta Oyle is again found driving her '86 Yugo down Lake Avenue, leaving the following trail of oil drops on the pavement.

If her car is moving from right to left, then ...

1. her velocity has a rightward direction and her acceleration has a rightward direction.
2. her velocity has a rightward direction and her acceleration has a leftward direction.
3. her velocity has a leftward direction and her acceleration has a rightward direction.
4. her velocity has a leftward direction and her acceleration has a leftward direction.

The velocity-time graph below depicts the motion of an automobile as it moves through Glenview during rush hour traffic. Use the graph to answer questions #22 - #26.

22. Determine the displacement of the automboile during the following intervals of time. PSYW

Do area calculations to determine the displacements.

 t = 0 s - 5 s t = 5 s - 15 s t = 15 s - 20 s Area of the pink triangle: A = 0.5*b*h A = 0.5*(5 s)*(10 m/s) A = 25 m Area of the green rectangle: A = b*h A = (10 s)*(10 m/s) A = 100 m Area of the blue triangle plus purple rectangle: A = 0.5*b1*h1 + b2*h2 A = 0.5*(5 s)*(5 m/s) + (5 s)*(5 m/s) A = 12.5 m + 25 m A = 37.5 m

23. Determine the velocity of the automobile at the following instant(s) in time.

Read velocity values off the velocity-time graph.

 t = 3 s t = 8 s t = 17 s v = 6.0 m/s v = 10.0 m/s v = 8.0 m/s

24. Determine the acceleration of the automobile during the following intervals of time.

Do slope calculations to determine the acceleration. Slope is rise/run.

 t = 0 s - 5 s t = 5 s - 15 s t = 15 s - 20 s a = slope = rise/run a = (10 m/s)/(5 s) a = 2.0 m/s/s a = slope = rise/run a = (0 m/s)/(10 s) a = 0.0 m/s/s a = slope = rise/run a = (-5 m/s)/(5 s) a = -1.0 m/s/s

25. Using complete sentences and the language of physics, describe the motion of the automobile during the entire 20 seconds. Explicitly describe any changes in speed or direction which might occur; identify intervals of time for which the automobile is at rest, the automobile is moving with constant speed, or the automobile is accelerating.

26. Supposing the automobile has an oil leak, demonstrate your understanding of its motion by drawing an oil drop diagram for the 20 seconds of motion. Divide the diagram into three distinct time intervals (0-5 seconds, 5-15 seconds, 15-20 seconds).

27. Convert the following position-time graphs to velocity-time graphs. For each graph, describe the motion in words.

28. Convert the following velocity-time graphs to position-time graphs. For each graph, describe the motion in words.

For practice with kinematic equations, see Lesson 6 of Unit 1 of The Physics Classroom. There you will see 20 problems with answers and written explanations.

For additional practice with graphical description of motion, see the Graphing Practice page. There you will see 37 problems with answers and written explanations.

### Unit 1 Review

Comments and suggestions can be sent by e-mail to Tom Henderson.

This page last updated on September 17, 1998.