Physics 0110 Midterm #3 Name ____________________________

Instructions: Make sure your first name, last name and PeopleSoft number are written on the scantron sheet, and write your name and recitation section on all of your workbooks as well as this exam document. This exam consists of eight multiple choice questions and three essay questions. Mark your multiple-choice answers in the supplied scantron sheet using a #2 pencil. Write answers to the essay questions in the supplied workbook, clearly indicating where your answers are by a surrounding box. You may use the workbooks as scratch paper for the multiple-choice questions, but please make sure the grader knows where your essay answers are located. You may use three 3"x5" double-sided notecards with handwritten notes. You may also use calculators, but you will need to show how you obtained your answers to receive full credit for the essay questions. Please read through all of the questions first, looking on both front and back of every page, so that you do not miss anything. Before leaving, don't forget to hand in everything (scantron sheet, workbooks, exam document).

1. Three children are pulling on a rotatable platform on a playground. The platform has a radius of 3.80 m. In the picture, two children are pulling with equal forces of 40.0 N in an attempt to make the platform rotate clockwise. The third child applies a force of 60 N as shown. What is the net torque on the platform? Note: “ccw” is counterclockwise and “cw” is clockwise.

A) 76 N m, ccwB) 76 N m, cwC) 290 N m, ccwD) 290 N m, cwE) 0 N m

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2. The density of the liquid flowing through the horizontal pipe in the drawing is 1200 kg/m3. The speed of the fluid at point A is 7.5 m/s while at point B it is 11 m/s. What is the difference in pressure, PB – PA, between points B and A?

A) –1.9 103 PaB) +3.8 103 PaC) –2.5 104 PaD) +5.0 104 PaE) –3.9 104 Pa

3. A satellite follows a circular path with constant speed around a planet. Which one of the following quantities is constant and non-zero for this satellite?A) linear velocityB) angular velocityC) centripetal accelerationD) angular accelerationE) total acceleration

4. A 1.0-m roulette wheel reaches a maximum angular speed of 18 rad/s before it begins decelerating. After reaching this maximum angular speed, it turns through 35 revolutions (220 rad) before it stops. How long did it take the wheel to stop after reaching its maximum angular speed?A) 12 sB) 48 sC) 3.7 sD) 8.8 sE) 24 s

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5. Three blocks, labeled A, B, and C, are floating in water as shown in the drawing. Blocks A and B have the same mass and volume. Block C has the same volume, but is submerged to a greater depth than the other two blocks. Which one of the following statements concerning this situation is false?

A) The density of block A is less than that of block C.B) The buoyant force acting on block A is equal to that acting on block B.C) The volume of water displaced by block C is greater than that displaced by block

B.D) The buoyant force acting on block C is greater than that acting on block B.E) The volume of water displaced by block A is greater than that displaced by block

B.

Use the following to answer question 6:

A relaxed spring protrudes from an opening 0.0500 meters as shown in Figure A.A 1.00-kg block is found to just force the spring completely into the opening as shown in Figure B.

6. How much potential energy is stored in the spring in Figure B?A) 0.245 JB) 0.490 JC) 4.90 JD) 9.80 JE) zero J

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7. A ball of mass M moves in a circular path on a horizontal, frictionless surface. It is attached to a light string that passes through a hole in the center of the table. If the string is pulled down, thereby reducing the radius of the path of the ball, the speed of the ball is observed to increase. Complete the following sentence: This occurs because

A) the linear momentum of the ball is conserved.B) it is required by Newton's first law of motion.C) the angular momentum of the ball is conserved.D) the angular momentum of the ball must increase.E) the total mechanical energy of the ball must remain constant.

8. A cable stretches by an amount d when it supports a crate of mass M. The cable is replaced by another cable of the same material having the same length and twice the diameter. If the same crate is supported by the thicker cable, by how much will the cable stretch?A) d/4B) d/2C) dD) 2dE) 4d

9. (15Points) A pottery wheel of radius 0.3 m is initially spinning with an angular speed of 8.0 rad/s. The angular speed is then increased to 12 rad/s over the next 4.0 seconds. Assume that the angular acceleration is constant.

(a) What is the magnitude of the angular acceleration of the pottery wheel?

(b) How many revolutions does the pottery wheel make during that 4.0 second interval?

10. (15 Points) A child standing on the edge of a freely spinning merry-go-round moves quickly to the center. (a) What is the net torque acting on the system (child plus merry-go-round)? (b) What happens to the angular speed of the merry-go-round? (c) What happens to the moment of inertia?

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11. (30 Points) A glass tube has several different cross-sectional areas with the values indicated in the figure. A piston at the left end of the tube exerts pressure so that mercury within the tube flows from the right end with a speed of 8.0 m/s. Three points within the tube are labeled A, B, and C.

Notes: The drawing is not drawn to scale.Atmospheric pressure is 1.01 105 N/m2; and the density of mercury is 13 600 kg/m3.

(a) At what speed is mercury flowing past the point labeled A?(b) What is the total pressure at point A?(c) At what speed is mercury flowing past the point labeled B?(d) What is the total pressure at point B?(e) What is the total pressure at point C?(f) What is the height h in the mercury manometer with the evacuated upper end?

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Answer Key

1. B2. E3. B4. E5. E6. A7. C8. A9.

10.11.

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