1
Fall 2006
Physics 16
Exam #2
Wednesday, November 1,7-10 pm
1. This is a closed book exam.
2. You can use a calculator.
3. This exam has a 3 hour time limit. The exam has 5 questions. Budget your time
accordingly. Do not get bogged down on any one question. They are meant to be
relatively straight-forward, but you may find some harder than others.
4. Please write legibly and explain your reasoning briefly including iiny assumptions
5. Do your work on these sheets or in a blue book. Tell me explicitly if I'm to look at
blue book.
6. Again, explain your work. You need not write in full sentences and colorful prose,
but make clear to me the logic and methods you're utilizing. Use diagrams, words
and equations, organized in a way I can follow. Draw free body diagrams where
appropriate (for this exam, I suggest that you draw a free body diagram for every
problem), specify your system, and make sure I can understand what your symbols
mean. Identify action-reaction pairs if you invoke Newton's Third Law.
7. If you have questions, come ask me. There's no need to try to guess my intent. And
don't panic.
Problem
1.
2.
3.
4.
5,
Total
Possible Score
20
20
20
20
20
100
1. An object of mass M is accelerated upwards with an acceleration a by the applied
force F. Find the tension in each rope and the magnitude of F in terms of acceleration a
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2. A bag of cement with mass 50 kg hangs from three wires. Two of the wires make an
angle with the horizontal, as shown: 0,=60 degrees, 02=25 degrees. Find the tensions
TI, T2 and T3 in the wires.
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3. Tarzaq who weighs 688N, swings from a cliff at the end of a convenient vine that is
18 m long. From the top of the cliff to the bottom of the swing, he descends by 3.2 m.
He gives himself a push, so that his initial speed along the circular trajectory is 2 m/s.The
vine will break if the force on it exceeds 1200 N. (a) Does the vine break? (b) If no, what
is the greatest force on it during the swing? If yes, at what angle with the vertical does it
break?
4. A box of mass m is pushed .
a with the horizontal. The
coefficient of kinetic fiction between the box and the ramp is pk; the coefficient of static
fiction is p,. How far up the ramp will the box move before stopping? How long will it
take to come to rest? What is the maximum angle that the ramp can have such that the
box, once stopped, will not start sliding back down the ramp?
5. A single bead slides with negligible fiiction on a wire that is bent into a circular loop
of radius r. The wire circle is always in avertical plane and rotates steadily about it
vertical diameter with a period T. The bead moves in a horizontal cjrcle at constant
speed. The position of the bead is described by angle 8 (take 0 4 <W2) that the radial
line, from the center of the loop to the bead, makes with the vertical. At what angle up
from the bottom of the circle can the bead stay motionless relative to the turning circle?