PH2100 - Michigan Technological University



PH2100 EXAM 1 Spring 2002

INSTRUCTIONS

1. Write your name, student identification number and recitation section on the appropriate spaces provided on the answer sheet.

2. With the exception of the included fresh equation sheet, no other equation sheets, papers, books, handbooks or tables are permitted.

3. No materials, including calculators, may be exchanged during the exam.

4. Keep your eyes on your own papers.

5. Units are an important part of numerical answers; be sure to include units on your answers.

6. Report all numerical answers to three significant figures unless the problem specifically instructs otherwise.

7. Vectors should be reported using [pic] unit-vector notation, unless otherwise instructed.

8. Write answers on your answer sheet as you work. Don’t wait until the end to copy your answers over. All answers have equal weight of 5 points each.

9. There are a total of 110 possible points on the exam. It will be graded out of 100 points total (although scores over 100 will be set equal to 100).

10. At the end of the exam, turn in only your answer sheet. Keep the rest of your exam for redemption work.

Recitation Section Time Instructor

R01 TR 0805-0855 D. Gao

R02 TR 0905-0955 R. Nemiroff

R03 TR 0905-0955 G. Agin

R04 TR 1005-1055 E. Nadgorny

R05 TR 1005-1055 C. Zhou

R06 TR 1105-1155 U. Hansmann

R08 TR 1205-1255 R. Nemiroff

R09 TR 1205-1255 C. Zhou

R10 TR 1305-1355 G. Agin

R11 TR 1305-1355 Y. Yap

R12 TR 1405-1455 R. Nemiroff

R13 TR 1405-1455 C. Zhou

R14 TR 1505-1555 R. Nemiroff

R15 TR 1505-1555 Y. Yap

R16 TR 1005-1055 R. Vanga

PROBLEMS

1. A student walks 1.02 km from her dorm room to the main doors of Fisher hall for her 8:05 am physics recitation. Once at the building doors, she walks an additional 0.214 km through the building to the classroom, and finally, 4.67 m to her desk. Following the rules for significant figures, calculate the total distance the student traveled from the dorm to her desk. Give your answer in meters and use proper scientific notation.

2. Using the latest in laboratory demonstration technology, Jerry makes a moving cart demonstration such that the cart’s displacement as a function of time is given by the following equation:

x(t) = 3.13 t2 + 8.55t

Here, x is in meters, t is in seconds.

a) Find the instantaneous velocity of the cart at time t = 2.22 s.

b) Find the instantaneous acceleration of the cart at time t = 0.00 s.

3. A car making a 100.0-km journey travels 40.0 km/hr for the first 50.0 km. How fast must it go during the second 50.0 km to have an average speed of 50.0 km/hr?

4. A student on the ground throws a set of keys vertically upward to her sorority sister who is at a window above her. It just so happens that the sorority sister at the window catches the keys just as they reach the maximum height of their vertical motion. If the keys were caught 1.55 seconds after they were thrown, at what initial speed were the keys thrown?

5. An absentminded physics professor crosses US 41 in front of Fisher Hall without watching the traffic. Fortunately, the driver of an oncoming car saw the professor and slammed on his brakes. No one got hurt, but the car made a skid mark 2.23 m long. If the car was initially traveling 13.3 m/s , what is the magnitude of the car’s deceleration (assumed to be constant) while the brakes were applied? Give your answer in m/s2 units.

6. An Alaskan rescue plane drops a package of emergency rations to a stranded party of explorers, as shown in the figure. Assume you can ignore air resistance. The plane is traveling horizontally at 43.5 m/s, is 113.0 m above the level ground, and drops the package when it is directly above the explorers.

a) What is the distance D that the package strikes the ground relative to the explorers? Assume the explorers don’t move until the package hits the ground.

b) What is the speed of the package just before it strikes the ground?

c) What is the direction of the package’s velocity just before striking the ground? (Following standard convention, give your answer as an angle in degrees from the positive x-axis going counter-clockwise.)

7. A child is playing with his yo-yo (a 0.299 kg mass on a 0.525 m string). Instead of using it properly, however, he is swinging it around and around in a vertical circle. At one particular instant, the yo-yo is moving downward in its circular path with a speed v = 3.19 m/s , while the string is parallel to the ground (see figure).

At this instant, find:

a) The magnitude of the centripetal acceleration of the yo-yo.

b) The magnitude of the total acceleration of the yo-yo.

8. A boat is trying to cross a wide river to reach the dock. As shown in the figure, the dock is directly north of the initial starting position of the boat. The river is moving with a uniform speed of vrE = 6.26 km/h relative to the Earth due east. If the boat travels at 9.26 km/h relative to the water,

a) what direction should be boat be heading in order that it travel due north and make it to the dock? Give your answer as an angle in degrees and specify either “east of north” or “west of north”.

b) If the river is 0.626 km wide, how long does it take the boat to reach the dock if it succeeds in traveling due north.

9. A block of mass 5.25 kg is resting in equilibrium on a frictionless surface inclined 30° up from the horizontal. It is suspended by a rope running parallel to the surface as shown in the figure.

a) What is the weight of the block?

(b) What is the magnitude of the normal force on the block due to the incline?

MULTIPLE CHOICE

10. A speck of dust on a compact disk, a distance R from the center, undergoes uniform circular motion with speed v. Over the time in which the particle makes one complete revolution, which of the following statements are true?

(a) The total displacement is zero; the average acceleration is v2/R; the magnitude of the average velocity is v.

(b) The total displacement is 2πR; the average acceleration is v2/R; the magnitude of the average velocity is v.

(c) The total displacement is 2πR; the average acceleration is v2/R; the magnitude of the average velocity is zero.

(d) The total displacement is 2πR; the average acceleration is zero; the magnitude of the average velocity is zero.

(e) The total displacement is zero; the average acceleration is zero; the magnitude of the average velocity is zero.

11. Two golf balls, projected at different times so they don’t collide, have trajectories A and B as shown in the figure. Which statement is correct (ignoring air resistance)?

(a) The initial velocity of ball B must have been greater than ball A.

(b) Ball B must be in the air longer than ball A.

(c) Ball A must be in the air longer than ball B.

(d) Ball A has greater acceleration than ball B.

(e) Ball B has greater acceleration than ball A.

12. A car is traveling due north with constant velocity for a long period of time. Imagining the car as a point particle, which of the following statements is true?

(a) Since the car is moving with constant velocity the car cannot be in equilibrium.

(b) Since the car is moving with constant velocity the net force acting on it is zero.

(c) Since the car is moving with constant velocity there are no forces acting on it.

(d) The car may be moving with constant speed but might still be changing direction as it moves.

(e) The driver must have fallen asleep.

13. A book is placed on a chair. Then a videocassette is placed on the book. The book exerts a normal force:

(a) on the floor, chair and videocassette.

(b) on the chair and the videocassette only.

(c) only on the videocassette.

(d) only on the chair.

(e) only on the objects that you have defined to be part of the system.

(f) on nothing because it is in equilibrium.

14. Can the magnitude of a particle’s displacement be greater than the distance traveled?

a) Yes

b) No

15. The apparent weight of a person in an elevator is greatest when the elevator:

(a) moves downward at constant velocity

(b) moves upward at constant velocity

(c) is not moving

(d) accelerates downward

(e) accelerates upward

16. An object moves in a straight line with constant acceleration, starting from rest. If the object moves a distance d in the first 1.00 second, how far will the object have moved in the first 3.00 seconds?

a) 1.50 d

b) 3.00 d

c) 4.50 d

d) 6.00 d

e) 9.00 d

ANSWER SHEET

Name:

ID# Recitation Section #

1.

2. (a)

(b)

3.

4.

5.

6. (a)

(b)

(c)

7. (a)

(b)

8. (a)

(b)

9. (a)

(b)

10. a b c d e

11. a b c d e

12. a b c d e

13. a b c d e f

14. a b

15. a b c d e

16. a b c d e

Raw Score:

Redemption:

Total Score:

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