Exam 3 Solution - real past exam PDF

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BINGHAMTON UNIVERSITY Department of Physics, Applied Physics and Astronomy S O L U T I O N

PHYS 121: Midterm Exam #3

Monday November 21, 2016

Fall 2016

If you want your exam returned to you, Print your Discussion Instructor’s LAST name:

INSTRUCTIONS: 1. Carefully read all problems and solve all of them. Box your answers. Observe the point value for each problem, as they may differ. All 3 long answer problems must be done in pen; failure to do so will result in forfeiting your access to a re-grade. All final answers for multiple choice must be placed in your bubble sheet, using a #2 pencil. You will not receive credit for the multiple-choice if you do not bubble in your name on that sheet. 2. It is your responsibility to print your name on ALL pages of this exam. For grading, the exam will be separated & pages could get mixed up if your name is not clearly printed at the top of all pages, resulting in a lower grade. 3. Answers to each problem should be written on the specific sheet that contains the question. Use both sides of the same sheet for your answers. Anything placed on a different page will not be graded. Any scrap paper given to you will be discarded; do not use this for your answers. 4. Show all your work and reasoning to receive full credit. Be sure your work is clearly shown, and your answers are circled with appropriate units. Don’t make the graders guess what you are trying to convey. 5. Cross out all unwanted work, as incorrect statements may cost you points. 6. This examination is to be taken without the aid of notes, textbook, electronic device (save non-alphanumeric calculators), or any other individual. Any violations of this condition will be referred to the Academic Honesty Committee, and this particular exam will earn no credit, without the option for grade replacement. 7. If a problem has multiple parts, and a latter part requires an answer from an earlier part for which you could not solve, state an assumed answer for the earlier part, and use it in the latter part. 8. You may use one side of a hand-written 3x5 note card for pertinent information. This note card may NOT contain solved examples problems, solutions to examples problems, or special cases pertaining to specific examples. This note card is a privilege, not a right and can be revoked. 9. You cannot leave early from the first Discussion section. You cannot enter the 2nd Discussion section more than 5 minutes late; if you are more than 5 minutes late – you forfeit your exam and the score becomes a zero. Possible Useful Information: For ax 2  bx  c  0 , x 

sin2   cos2  1

b  b 2  4ac 2a tan  

g =9.8 m/s2 toward Earth’s center Along the surface of the earth:

cos 2   sin 2   cos 2

sin  cos

1 sin  cos   sin2 2

G=6.67E-11 Nm2/kg2 North (+y)

sin 45 

1 2

Vertically upward (toward the sky): out of the page (+z)

West (-x)

East (+x) Vertically downward (toward the ground): into the page (-z)

South (-y) 1

Part I: Multiple Choice Section (2.5 points each) Last Name

First Name

Answer in #2 Pencil on your bubble sheet. Fill in your name on the bubble sheet (LAST NAME FIRST) & BUBBLE it also for credit on this section. You may write on the multiple choice questions, but only the bubble sheet will be graded, and retained. Each question is worth 2.5 points. Choose the closest answer. Some questions may have 4 choices, others 5.

1. Consider a uniform hoop of radius R and mass M rolling without slipping (Ihoop = MR2). Which is larger, its translational kinetic energy or its rotational kinetic energy? A) Translational kinetic energy is larger. B) Rotational kinetic energy is larger. C) Both are equal. D) You need to know the speed of the hoop to tell.

2. A person sits on a freely spinning lab stool that has no friction in its axle. When this person extends her arms, A) her moment of inertia decreases and her angular speed increases. B) her moment of inertia decreases and her angular speed decreases. C) her moment of inertia increases and her angular speed increases. D) her moment of inertia increases and her angular speed decreases. E) her moment of inertia increases and her angular speed remains the same.

3. When you ride a bicycle, in what direction is the angular velocity of the wheels? A) to your left B) to your right C) forwards D) backwards

E) up

4. A bicycle has wheels that are 60 cm in diameter. What is the angular speed of these wheels when it is moving at 4.0 m/s? A) 1.2 rad/s B) 4.8 rad/s C) 0.36 rad/s D) 13 rad/s E) 7.6 rad/s

5. A 15-kg child is sitting on a playground teeter-totter, 1.5 m from the pivot. What is the magnitude of the minimum force, applied 0.30 m on the other side of the pivot, that is needed to make the child lift off the ground? A) 75 N B) 740 N C) 23 N D) 44 N E) 66 N 6. 50-cm3 block of wood is floating on water, and a 50-cm3 chunk of iron is totally submerged in the water. Which one has the greater buoyant force on it? A) the wood B) the iron C) Both have the same buoyant force. D) It cannot be determined without knowing their densities.

7. The deepest point of the Pacific Ocean is 11,033 m, in the Mariana Trench. What is the gauge pressure in the water at that point? The density of seawater is 1025 kg/m3. A) 5.55 × 107 Pa B) 8.88 × 107 Pa C) 1.11 × 108 Pa D) 2.22 × 108 Pa E) 3.33 × 108 Pa 8. A 500-N weight sits on the small piston of a hydraulic machine. The small piston has an area of 2.0 cm2. If the large piston has an area of 40 cm2, how much weight can the large piston support? Assume the pistons each have negligible weight. A) 25 N B) 500 N C) 10000 N D) 40000 N

9. Fluid flows at 2.0 m/s through a pipe of diameter 3.0 cm. What is the volume flow rate of the fluid? A) 1.4 × 10-3 m3/s B) 5.7 × 10-3 m3/s C) 14 m3/s D) 57 m3/s 10. If the frequency of a system undergoing simple harmonic motion doubles, by what factor does the maximum value of acceleration change? A) 4 B) 2 C) D) 2/π

2

PHYS 121

For Graders Only

Answer in PEN Midterm III Monday, Nov. 21, 2016

, Last Name

First Name

[25 Pts] 1. A wrench is used to loosen a nut (negligible mass) from a bolt as seen below. The wrench length is

L=0.315m and mass M=3.32kg. A force F=101N is applied to the end of the wrench perpendicular to its length to loosen the nut. Friction acts at L/10 from the axis of rotation, where the nut squeezes the bolt with a force F0=2,250N (effectively a normal force). The wrench functions as a rod rotating about its end. The moment of inertia for a rod about its center of mass is given by Icm= 1/12 mL2. All torques are to be calculated relative to the axis of rotation. a) The nut just begins to loosen (turn). Calculate the coefficient of static friction (μs) between the nut and bolt. b) Derive an expression for the moment of inertia of the wrench about it’s end. c) Once the nut is loosened the kinetic friction reduces to 1/12 the static value. Calculate the angular acceleration of the wrench. d) With the wrench starting from rest, determine the angle θradians it rotates through until it picks up an angular velocity of 725 rad/s. e) Caculate the change in angular momentum of the wrench in 0.530 seconds. For these speeds, it must be a power tool – which is of no consequnce in solving the problem. 5pt

L L 10F 10(101)   0.449 Ff max  0  LF  s F0  s  10 10 2,250 F0 L  LF  F f  10

a )  AOR  LF 

F   Ff 4pt

b) I end  I cm  md 2 

1 1 L ML2  M ( ) 2  ML2 12 2 3

2

This evaluates to 0.110 kgm

6pt

c)   AOR  LF 

L (0.449)(2,250) 1 2 L F f max  I  LF   ML  10 12 10 12 3

101  8.419  92.58  0.3486

   265.58  266

rad s2

4pt

d)  2  02  2  725 2  0  2(265 .58 )( )    989 .6  990 . rad

6pt

e)

L 1 1   Text   F   Ff  I  ML2 ( )  (3.32)(.315 2 )[265.58]  29.163 t 3 3

kgm2 L  (29.163)(0.530 s)  15.456  15.5 s...