# PHY102 Motion Exercises week 1

PHY-102: Motion Exercises

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Complete the following exercises.

1. Jane is collecting data for a ball rolling down a hill. She measures out a set of different distances and then proceeds to use a stopwatch to find the time it takes the ball to roll each distance.

a. What is the independent variable in her experiment?

b. What is the dependent variable in her experiment?

c. Give one control variable for her experiment.

2. Consider an experiment where you drop an object.

a. Briefly describe your proposed experiment. (Make sure it is controlled).

b. What would be the independent variable for your experiment?

c. What would be the dependent variable for your experiment?

d. Give one control variable for your experiment.

3. Consider a freely falling object.

a. What is the acceleration (in m/s2) after 5 seconds of fall?

b. What is the acceleration (in m/s2) after 10 seconds of fall?

c. What is the velocity (in m/s) after 5 seconds of fall?

d. What is the velocity (in m/s) of 10 seconds of fall?

4. A sign is hung between two cables as illustrated below. If the sign weighs 350 N, what is the tension (in N) in each cable?

5. A construction worker on a high-rise building is on a platform suspended between two cables as illustrated below. The construction worker weighs 850 N, the plank weighs 450 N, and the tension in the left cable is 550 N.

a. What is the tension (in N) in the right cable?

b. Explain your answer.

6. Two forces of 50 N and 30 N, respectively, are acting on an object. Find the net force (in N) on the object if

a. the forces are acting in the same direction

b. the forces are acting in opposite directions.

7. A box is pulled straight across the floor at a constant speed. It is pulled with a horizontal force of 48 N.

a. Find the net force (in N) on the box.

b. Find the force of friction (in N) from the floor on the box.

c. The person pulling on the box stops pulling and the box comes to a rest. Find the force of friction (in N) on the box when at rest.

8. A bowling ball rolls 32 meters in 0.8 seconds. Find the average speed (in m/s) of the bowling ball in m/s.

9. A car accelerates from 3.5 m/s to 17 m/s in 4.5 seconds. Find the acceleration of the car in m/s2.

10. Rank the following from lowest to highest:

a. The support force on you standing in an elevator at rest.

b. The support force on you standing in an elevator accelerating upward.

c. The support force on you standing in an elevator accelerating downward.

11. Describe the speed and acceleration of the ball released from the top of the track shown in the figure below.

12. Describe the speed and acceleration of the ball released from the top of the track shown in the figure below.

13. Describe the speed and acceleration of the ball released from the top of the track shown in the figure below.

14. You throw a ball upward with a speed of 14 m/s. What is the acceleration of the ball after it leaves your hand? Ignore air resistance and provide an explanation for your answer.

15. How would your answer to the previous question change if you take into account the effects of air resistance?

16. Describe the speed and acceleration of a person sky diving. Include in your explanation a description of the motion before the parachute is opened as well as a description of the motion after the parachute is opened.

17. A net force of 24 N is acting on a 4.0-kg object. Find the acceleration in m/s2.

18. A person pulls horizontally with a force of 64 N on a 14-kg box. There is a force of friction between the box and the floor of 36 N. Find the acceleration of the box in m/s2. Show your work.

The remaining questions are multiple-choice questions:

19. One difference between a hypothesis and a theory is that a hypothesis

A. is a guess that has not been well tested, whereas a theory is a synthesis of well-tested guesses.

B. is testable, whereas a theory is not testable.

C. can be revised, whereas a theory cannot be revised.

D. is not testable, whereas a theory is testable.

20. A car starts from rest and reached a speed of 24 m/s in 6 seconds. What is the acceleration of the car?

A. 144 m

B. 6 m/s2

C. 4 m/s2

D. 10 m/s2

E. 0 m/s2

21. Which of the following forces is NOT a contact force?

A. Friction force

B. Support force

C. Force of gravity

D. Tension force

22. If you pull horizontally on a desk with a force of 150 N and the desk doesn’t move, the friction force must be 150 N. Now if you pull with 250 N so the desk slides at constant velocity, the friction force is

A. more than 150 N, but less than 250 N.

B. 250 N.

C. more than 250.

23. Suppose a particle is accelerated through space by a constant 10 N force. Suddenly the particle encounters a second force of 10 N in a direction opposite to that of the first force. The particle

A. is brought to a rapid halt.

B. theoretically accelerates to speeds approaching the speed of light.

C. continues at the speed it had when it encountered the second force.

D. gradually slows down to a halt.

24. Newton’s First Law of Motion applies to

A. objects at rest only.

B. moving objects only.

C. both moving and nonmoving objects.

25. A freely falling object starts from rest. After falling for 2 seconds, it will have a speed of about

A. 5 m/s

B. 10 m/s

C. 20 m/s

D. 40 m/s

26. Suppose an object is in free fall. Each second the object falls

A. the same distance as in the second before.

B. a larger distance than in the second before.

C. with the same instantaneous speed.

D. with the same average speed.

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