Fall 2000 Physics 101 Hour Exam 3
(25 questions)

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This exam consists of 25 questions; true-false questions are worth 2 points each, three-choice multiple choice questions are worth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 114. When the exam was given, the mean was 92.8; the median was 96. Click here to see the formula sheet that came with the exam.


This and the next question pertain to the following physical situation:

A metal block of volume 0.02 m3 and of density r = 5000 kg/m3 is suspended under water (density=1000 kg/m3). What is the tension in the string?

(a)   375 N
(b)   550 N
(c)   784 N
(d)   1100 N
(e)   0 N


Suppose the answer to the previous problem is T. Now suppose that the water is replaced with oil, which has density 800 kg/m3 (i.e., less than that of water). The tension in the string will now be

(a)   less than T.
(b)   equal to T.
(c)   greater than T.


Consider two identical containers. Container A is filled with water to a certain level. Container B has a block of wood floating in it, but the level of the water is the same as in container A. Which container weighs more?

(a)   Container A
(b)   Container B
(c)   They both weigh the same.


A man floats in the ocean with 90% of the volume of his body below the surface. The density of the ocean water is 1025 kg/m3. What is the average density of the man?

(a)   704 kg/m3
(b)   923 kg/m3
(c)   846 kg/m3
(d)   1522 kg/m3
(e)   1250 kg/m3


A U-shaped tube is open at both ends to the atmosphere. It contains two different liquids. One liquid has density r = 1000 kg/m3. The other liquid has density r1 = 1200 kg/m3. The height h is 0.30 m (see the figure, which is not necessarily to scale). What is the height h1?

(a)   0.15 m
(b)   0.20 m
(c)   0.25 m
(d)   0.30 m
(e)   0.36 m


The pressure on the roof of a tall building is 0.993 × 105 Pa and the pressure on the ground is 1.010 × 105 Pa. The density of air is 1.29 kg/m3. What is the height of the building?

(a)   27 m
(b)   68 m
(c)   99 m
(d)   134 m
(e)   156 m


A hydraulic lift is used to lift a block of mass M. The block rests on the right massless plunger. A force F1 is applied to the left massless plunger. The two plungers are at the same height. The diameter of the left cylinder is D1 and the diameter of the right cylinder is D2. What force F1 is required to lift the block?

(a)   Mg
(b)   Mg(D1/D2)
(c)   Mg(D2/D1)
(d)   Mg(D1/D2)2
(e)   Mg(D2/D1)2


This and the next question pertain to the following physical situation:

Water (density = 1000 kg/m3) flows in a horizontal circular pipe from a region of larger cross section (A) to smaller cross section (B), as shown in the figure below. The cross sectional area of B is 0.25 × 10-3 m2, the speed of the water in B is 16 m/s, and the speed of the water in A is 4 m/s. What is the cross sectional area of A?

(a)   0.50 × 10-3 m2
(b)   1.00 × 10-3 m2
(c)   4.00 × 10-3 m2


Which of the following statements is true about the pressures PA and PB?

(a)   PA = PB
(b)   PA > PB
(c)   PA < PB


This and the next three questions pertain to the following physical situation:

A small solid cylinder of mass M and radius R is released from rest at the top of a hill. The height of the hill is H. The cylinder rolls without slipping down the hill. Assume no energy is lost to friction.

When the cylinder is part of the way down the hill, the magnitude of its acceleration is a. What is the magnitude of the torque about an axis through the center of the cylinder due to the static friction between the cylinder and the surface?

(a)   MR2a
(b)   MRa/2
(c)   MRa
(d)   MR2a/4
(e)   MRa/4


The total kinetic energy (translational plus rotational) of the cylinder at the bottom of the hill is

(a)   greater than MgH.
(b)   equal to MgH.
(c)   less than MgH.


You are now given that M = 2 kg, R = 0.25 m, and H = 20 m. What is the speed of the cylinder at the bottom of the hill?

(a)   18.1 m/s
(b)   12.4 m/s
(c)   16.2 m/s
(d)   24.3 m/s
(e)   32.5 m/s


Let your answer to the previous problem be V. Suppose instead that the solid cylinder is replaced by a hollow cylinder with the same radius and mass. The speed of the hollow cylinder at the bottom of the hill is

(a)   greater than V.
(b)   equal to V.
(c)   less than V.


A figure skater, initially spinning with some non-zero angular velocity, pulls her arms in, causing her moment of inertia to decrease. Which of the following quantities increase as a result?

(a)   angular velocity, angular momentum, and kinetic energy
(b)   angular velocity and kinetic energy only
(c)   angular velocity only


A student holding a bicycle wheel sits on a frictionless barstool. The wheel is initially spinning counter-clockwise in the horizontal plane, as viewed from above, and the barstool is not rotating. She now turns the wheel over, as shown in the figure below. What happens?

(a)   She starts to spin counter-clockwise.
(b)   She starts to spin clockwise.
(c)   Neither of the above


Disk A has moment of inertia 10 kg-m2 and initial angular velocity w = 20 rad/s about its axis. Disk B has moment of inertia 30 kg-m2 and is initially at rest. Disk A is then dropped onto Disk B so that they stick together and their axes line up. What is the angular velocity of the combined disks about their mutual axis?

(a)   5 rad/s
(b)   10 rad/s
(c)   15 rad/s
(d)   20 rad/s
(e)   25 rad/s


This and the next question pertain to the same physical situation:

The north stairwell in Loomis Lab contains a hook 12 m above ground level. A steel ball of mass 10 kg is suspended by a thin wire from the hook so that the ball sits just above the floor. The ball is pulled to the side, then released. With what period does it oscillate?

(a)   3.1 s
(b)   3.5 s
(c)   6.2 s
(d)   7.0 s
(e)   9.8 s


Suppose the mass of the steel ball is changed to 20 kg. What happens to the period of the pendulum?

(a)   It increases.
(b)   It decreases.
(c)   It stays the same.


This and the next question pertain to the same physical situation:

A slingshot is built from a single, massless elastic band with spring constant 64 N/m. The slingshot is stretched by 0.5 m from its relaxed position and loaded with an 0.01 kg stone. At what speed V will the stone leave the slingshot?

(a)   5 m/s
(b)   10 m/s
(c)   20 m/s
(d)   40 m/s
(e)   80 m/s


Suppose that the stone is replaced by another stone of mass 0.04 kg, but everything else remains the same. At what speed will this stone leave the slingshot, if the answer to the last problem is V?

(a)   V/4
(b)   V/2
(c)   V


A brass weight of mass 0.5 kg is suspended vertically from a spring of relaxed length 0.5 m. The brass weight stretches the spring to a new length of 1 m. What is the spring constant of the spring?

(a)   4.5 N/m
(b)   9.8 N/m
(c)   11.0 N/m
(d)   12.1 N/m
(e)   13.0 N/m


This and the next three questions pertain to the same physical situation:

A block of mass M = 10 kg is attached to a relaxed spring of spring constant k = 250 N/m on a horizontal frictionless surface. The opposite end of the spring is fixed to a wall, as shown in the figure. At time t = 0, the block is struck, giving it an initial velocity V0 = 2 m/s to the right. What is the maximum compression of the spring?

(a)   0.1 m
(b)   0.2 m
(c)   0.3 m
(d)   0.4 m
(e)   0.5 m


At what point during the oscillation is the kinetic energy of the block largest?

(a)   when the spring is relaxed
(b)   when the spring has its maximum compression
(c)   neither of the above


How long does it take for the mass to return to its initial position for the first time?

(a)   0.35 s
(b)   0.63 s
(c)   0.78 s
(d)   0.95 s
(e)   1.08 s


Suppose your answer to the previous problem is T. How will your answer change if the initial velocity is doubled?

(a)   It will increase.
(b)   It will decrease.
(c)   It will stay the same.