Physics 104- Spring 2013
Sample Questions for Lab Exam 2
1. Experiment station 1: A ball of mass m is tied to a string of length L and revolved
in a horizontal plane with the string making an angle of θ degrees with the vertical.
This is called a conical pendulum.
a. Draw a free body diagram and derive an equation for the tangential velocity
Vt of the ball in terms of the radius R, acceleration due to gravity g and
length L of the string. Call this tangential velocity the theoretical speed of
the ball.
b. Using the materials that are provided (tripod stand, steel ball, string stop
watch meter sticks) set up the conical pendulum.
c. Make the necessary measurement to determine the theoretical speed of
the ball from the equation derived in a). Present the information in an
appropriate table.
d. Now describe how you will measure the speed of the ball experimentally
using a stop watch. Present the data in a table.
e. Compare the theoretical speed with the experimental speed.
2. Experiment station 2: Balance a meter stick on a wedge or a knife edge. Suspend
a total mass of 200 grams 10 cm from the fulcrum. Suspend a 100 grams mass
on the opposite side of the fulcrum at an appropriate distance such that the meter
stick balances. Record the data in an appropriate table. Repeat this for at least 6
more sets of weights and distances.
a. Study your data table. Look for any pattern. Describe this pattern in word
statement.
b. Convert this word statement into a mathematical equation. Explain what
each symbol represents.
3. Two balls of mud collide head on in a perfectly inelastic collision. Suppose
m1=0.50 kg, m2=0.25 kg, v1i=+4.0 m/s and v2i==3.0m/s. Find the velocity of the
composite ball of mud after the collision.
4. At what maximum speed can a car negotiate a horizontal unbanked turn (radius =
51) in dry weather (coefficient of static friction = 0.95) and icy weather (coefficient
of static friction = 0.10)?.A labelled free body diagram is required. Show how the
free body diagram is used to get the expression for speed.
5. A disk of moment of inertia I1 is rotating freely with angular speed w1 when a
second non-rotating disk with moment of inertia I2 is dropped on it. The two then
rotate as a unit. Find the final angular speed w2? Note your answer will be in
symbolic form.
6. A uniform horizontal 300-N beam, 5.00 m long, is attached to a wall by a pin
connection that allows the beam to rotate. Its far end is supported by a cable that
makes an angle of 53.0° with the horizontal. If a 600-N person stands 1.50 m from
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the wall, find the tension in the cable and the force exerted by the wall on the
beam.
7. Suppose you missed a lab on Newton’s Second Law and you have arranged to do
a makeup lab on your own. The instructor has provided on your computer station
a 2 meter PASCO track, a super pulley, a Cart with a plunger, 80 grams of mass,
and a stop watch that can measure up to 100 of a second. You noticed that the
instructor did not provide the picket fence and the Photogates. You also know that
your instructor had to leave for another engagement and there is no one else to
help you secure additional equipment. You sit in the lab thinking how you are
going to complete the makeup lab with what whatever equipment you have. From
your knowledge of Newton’s second law you know that in order to do the
experiment you need to collect data on acceleration of the Cart for different
forces, while keeping the mass of the System constant. After some thought you
realize that you actually do not need the picket fence and Photogates to do the
experiment and that you can still measure the acceleration of the Cart for different
forces using the meter scale on the track and the digital stop watch. Answer the
following questions.
a. Write the equation that is applicable to this experiment to measure the
acceleration of the Cart.
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b. Suppose you performed the experiment and get the following data. Plot a
graph and show that it verifies the Newton’s second Law. What other
information can you obtain from it? Explain in detail all your analysis.
Force in Newton’s
Acceleration in m/s2
0.127
0.190
0.213
0.320
0.446
0.670
0.646
0.970
0.739
1.11
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