EXAM IPhys 172H Fall 2009

Modern Mechanics - HonorsInstructor: Prof. E. W. Carlson

TEST FORM “A”

Machine Answer Sheet (This part of the exam is worth 75 points.)

Using a pencil, fill in Last Name, First Name, and Middle Initial, plus your 10-digit PurdueUniversity ID number, which starts with 00. Enter “Carlson” for instructor, Course (PHYS172H), Date (9/17/09), and Test (1). Enter “Test Form” from the box above. Leave“Section” blank. You must include your Signature.

There are two parts to Exam I: The machine-graded part of this test, and the last page that you turn in to be graded by hand.

Hand-Graded Part: (This part of the exam is worth 25 points.)

Enter Name, Signature, PUID.

Your work must be legible and clear! Correct reasoning is required for full credit --a correct answer with incorrect or no reasoning will be counted as wrong.Cross out anything you do not want us to read in the hand-graded part.

Fill in only one answer per question. If your answer is slightly different,choose the closest answer. You must use a PENCIL and fill in the circle completely.

FINISHED? Turn in all parts of this exam to the front of the classroom,including question sheets and scratch paper. Show ID to the instructor or teaching assistant when turning in your exam.

Vectors

Problem 1. Vectors. Which statement is true about these vectors?

1)

2)

3)

4)

CORRECT

Each multiple choice question is worth 5 points.

Carnival Game

Problem 2. Carnival Game. To win the the following carnival game, you mustthrow a ball such that it goes through the cylinder on the left without touching the sides at all. That is, the ball must land in the cylinder with no horizontalcomponent to its velocity.

AB

C

At what angle should you throw the ball in order to win the game and takehome the giant teddy bear? (Neglect air resistance.)

1) Steeper than 45O 2) 45O

3) Less steep than 45O

4) This game is a scam, since it is not possible to win. CORRECT

Earth and Moon

Problems 3 and 4 are about the Earth and Moon. (Not to scale)

mEearth =6.0 x 1024 kg massREarth = 6.4 km radius

mMoon = 7.3 x 1022kgRMoon = 1.7 km

RE-M = 380,000 km Earth-moon distance

Problem 3. What is the magnitude of the force of gravity that the Moon exerts on the Earth? CORRECT 1) 2.0 x 1020 N

2) 5.6 x 10-20 N3) 8.4 x 1025 N4) -1.2 x 1020 N

Problem 4. How many electrons would you have to move from the Earth to the Moon for the magnitude of the electric force between the Earth and Moon to equal that of the gravitational force between them? Choose the closest answer. (There are about 1051 electrons in all of the atoms on Planet Earth.)

1) 10 electrons2) 1021 electrons

CORRECT 3) 1032 electrons4) 1048 electrons

Particle Decay

Problem 5. A stationary particle in otherwise empty space decays into two fragments. One of the fragments is obsesrved to have a momentum of <5.6, -4.3, 2.0> kg m/s just after the decay. The other particle is invisible to the detector and so its momentum cannot be directly measured. What is the momentum of the invisible particle?

1. <5.6, -4.3, 2.0> kg m/sCORRECT 2. <-5.6, 4.3, -2.0> kg m/s

3. <5.6, 4.3, -2.0> kg m/s4. <-5.6, -4.3, 2.0> kg m/s5. Not enough information is given

Bees

Problems 6-8 are about four bees, with the following velocities:

Bee A: <0,1,1> m/sBee B: <1,0,1> m/sBee C: <0,3,3> m/sBee D: <-1,1,1> m/s

Problem 6. Which of the bees fly with the same velocity? 1) only A & C2) only B & D3) only A & D4) A, B, & C

CORRECT 5) None of the bees fly with the same velocity

Problem 7. Which of the bees fly in the same direction?1) only A & B

CORRECT 2) only A & C3) B, C, & D 4) None of the bees fly in the same direction

Problem 8. Which of the bees fly with the same speed? 1) only C & D2) only A & D

CORRECT 3) only A & B4) None of the bees fly with the same speed

Bug and WindshieldProblems 9-11 are about the following scenario. The windshield of aspeeding car hits a hovering insect.

Problem 9. Compare the magnitude of the force that the car exerts on the bugto the force that the bug exerts on the car. (Note: the interatomic forcesbetween bug and windshield are electric forces.)

1) The force that the car exerts on the bug is bigger.CORRECT 2) The two forces are equal.

3) The force that the bug exerts on the car is bigger.

Problem 10. Compare the magnitude of the change of momentum of the bugto that of the car:

CORRECT 1) The magnitudes of the change of momentum are equal.2) The magnitude of change of momentum of the bug is bigger.3) The magnitude of change of momentum of the car is bigger.

Problem 11. Compare the magnitude of the change of velocity of the bug tothat of the car:

1) The magnitudes of the change of velocity are equal.2) The magnitude of change of velocity of the car is bigger.

CORRECT 3) The magnitude of change of velocity of the bug is bigger.

Blocks in SpaceProblems 12-14 are about the following scenario. In outer space, farfrom other objects, block 1 of mass 45 kg is at position < 9, 8, 0 > m,and block 2 of mass 1100 kg is at position < 17, 8, 0 > m.

Problem 12. What is the (vector) gravitational force acting on block 2due to block 1? It helps to make a sketch of the situation.

1) <0, -5.18 x 10-8, 0 > N2) < 8.02 x 10-7, 0, 0 > N

CORRECT 3) < -5.18 x 10-8, 0, 0 > N4) <0, 0, 8.02 x 10-7 > N

Problem 13. At 4.2 seconds after noon both blocks were at rest at thepositions given above. At 4.3 seconds after noon, what is the (vector)momentum of block 2?CORRECT 1) < -5.18 x 10-9, 0, 0 > kg·m/s

2) <0, 2.1 x 10-2, 0 > kg·m/s3) < 8.02 x 10-7, 0, 0 > kg·m/s4) < -5.18 x 10-9, 8.02 x 10-7, 0 > kg·m/s

Problem 14. At 4.3 seconds after noon, what is the (vector)momentum of block 1?

1) < 2.1 x 10-2, 0, 0 > kg·m/s2) < 3.9 x 10-5, 0, 0 > kg·m/s3) <0, 7.09 x 108, 0 > kg·m/s

CORRECT 4) < 5.18 x 10-9, 0, 0 > kg·m/s

Star and PlanetProblem 15.A star of mass 7 x 1030 kg is located at <5 x 1012, 2 x 1012 , 0> m.A planet of mass 3 x 1024 kg is located at <3 x 1012 , 4 x 1012, 0> mand is moving with a velocity of <0.3 x 104 , 1.5 x 104, 0> m/s.

What is the initial force due to gravity of the star on the planet?1) 9.2 x 1015 <0.7, -0.7 ,0> N2) 9.2 x 1015 <-0.7, 0.7, 0> N

CORRECT 3) 1.8 x 1020 <0.7, -0.7, 0> N4) 1.8 x 1020 <-0.7, 0.7, 0> N

Pool Game

Problem 16. (Hand Graded, 15 total points) You jump off of a platform, and catch a ball in mid-air. Your center of mass is at initial position <0,0,0>m. Just after youleave the platform, your initial velocity is <12,5,0>m/s. Your friend throws you a ball of mass 2kg, and you catch it in mid-air, when the y-component of your position again reaches ry = 0m. The velocity of the ball right before you catch it is <0,0,22>m/s.

PHYS 172H -- Fall 2009

Name (Print): __________________________

Signature: ____________________________PUID: _______________________________

Pool GameA) (5 points) What is your momentum just after you leave the platform? State your assumptions clearly. For the purposes of thisproblem, it is okay to lie about your own weight, but you should state a reasonable number.

Name ______________

Pool GameB) (10 poins) What is your momentum just after you catch the ball?

Name ______________

Pool Game continuedC) (10 poins) Approximately how long was your friend’s hand in contact with the ball in order to accelerate it to roughly 22m/s? State your assumptions and approximations clearly.

Name ______________

Constants and Equations

211

2

29

2

0

8

24

Earth

6

Earth

31

electron

27

proton

neutron proton

N?m6.7 10

kg

1 N?m9 10

4 C

3 10 m/s

9.8 N/kg

6 10 kg

6.4 10 m

9 10 kg

1.7 10 kg

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M

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1 kg = 2.2 pounds

1 inch = 2.54 cm

1 foot = 30.5 cm

1 mile = 1609 m

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Scratch Sheet