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Midterm
PHYS 2010, Spr~n,2009, Michelle Arnold
Name: ~,N(-'-';~=-'~/ I ~=--,,-----A-=..:...r---,--Y."V---,-(=cL~ Seat # (this is printed on the back of your seat): ___ _
Instructions: Time limit: 50 minutes. Answer all questions. Multiple choice: There is only one correct answer to each mUltiple choice questions. Circle the letter of the answer you choose, and make sure if you change your mind it is clear which of the two answers you want as your actual answer. Problems: Show all of your work.
Total Points Possible = 30
Multiple Choice [6 x 1.5 points each = 9 points]
- An analogy can be drawn between quantities that describe linear (translational) motion and quantities that describe rotational motion. What rotational quantity is analogous to "force" for linear motion?
a. angular velocity, co
£ b.^ angular acceleration,^ a. c. moment of inertia, I d. angular momentum, L Ci) torque, 't
- A large mass and a small mass both have the same linear momentum, p. Which mass has the greater velocity?
a. the large mass has the greater velocity
(bJ the small mass has the greater velocity
c. both masses have the same velocity d. not enough information is given to know which mass has the greater velocity
- A physics professor rotates a meter stick to demonstrate the concept of rotational inertia. She first rotates it by holding the meter stick in the center, and then she rotates it by holding it by one end. In which case does the meter stick have more rotational inertia?
a. in both cases the meter stick has zero rotational inertia b. the meter stick has more rotational inertia when it is held in the center and rotated
@ the meter stick has more rotational inertia when it is held at one end and rotated
d. the meter stick has the same rotational inertia whether it is held in the center or at one end e. not enough information is given to determine in which case the meter stick has more rotational inertia
- For an object to be in equilibrium, which of the following must be true?
a. the velocity of the object must be zero b. all forces must balance so that the net force is equal to zero c. all torques (clockwise and counter-clockwise) must balance so that the net torque is equal to zero d. a and b are both correct
@ band c are both correct
f. a, band c are all correct
- A 75 kg box is sitting at rest on a frictionless, horizontal surface. You push on the box with a horizontal force of 125 N for 1.8 seconds. What is the final speed of the box?
a. 0.333 mis FL:lC:::'Lf> b. 0.926 mis c. 1.08 mis GQ3mis e. none of the above (^) Vf--;: Fb-G -tv'
- Dr. Arnold is holding a bike wheel (moment of inertia = 1.2 kg_m^2 , radius = 0.4 m) horizontally. She applies a tangential 12.5 N force to the bike wheel for 1.8 seconds. What is the final angular
speed of the wheel? 'CDC. -;::.tOL
GJ 7.5 radls b. 10.8 radls c. 18.75 radls
d. 46.9 radls ~-;.~ G-be
A e.^ none of the above
::r :p
Short Answer OuestionslProblems
- [3 points] Dr. Arnold, assumed mass of 50 kg, and Dr. Carroll, assumed mass of 70 kg, are standing on a frictionless sheet of ice. When Dr. Arnold begins telling yet another story about her cute beagle Bailey Dr. Carroll gives her a shove and starts her moving at 1.3 mis to the left. What will be Dr. Carroll's speed after shoving Dr. Arnold?
50)'(\
PA~~ p+:
o -= ~OC-l ~S).fr)V
V -= .?OC(.~) .-;ro
- [4 points] Consider an experiment similar to one conducted in the rotational inertia lab. A disk (mass = 0.8 kg, radius = 0.18 m) is rotating at 15 rad/s. You then drop a long thin ruler (mass = 0.45 kg, length = 0.3 m) on the center of the disk, as illustrated below. What is the angular velocity of the rotating disk and ruler, after the ruler has been dro~ped? The moment of inertia for a disk rotating about its center is Y2MR , and the moment of inertia for a long thin rod (such as a ruler) rotating about its center is ~ ML
o
Find\ B
.If~.lM~ ;,;)... (^) ~-::. :r:"i5::: +- .....l...{-u \e r
:LA': ±(O.<g){O.\ot' (^) =4::-= O.()\aq(C, +-'Ji mt:"
~ --; OO\a'I" +t,.lO.'fS)(Or3,)1...
[~-O 0 .OI(()33'St'e-'("Til- 1
J..;.-;J..r;
LWJ ~~UJ.c
LI..: -= ~ W.A -:: r;ota.% \ (j')fo.d~~ -= ITt. q rcJ.1S ] ~ 'fO(:oG;5~)
- [4 points] A car is traveling at 19 mls when it slams on its breaks, coming to a stop in 7. seconds. If the radius of the car tires is 0.32 m, how many revolutions do the tires make while stopping?
So"~
L;X}-::o..:o.u-be
De- -::. laq· '=>qB .'5) ..
,lPe -= Oad.:tfriill (&~~ ) -z: [3'5' :Lf (evCJ~id\S I ,
