EXAM III, PHYSICS 1403
December 2, 2009, Dr. Charles W. Myles
INSTRUCTIONS: Please read ALL of these before doing anything else!!!
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4.
PLEASE put your name on every sheet of paper you use and write on ONE SIDE of the paper only!!
PLEASE DO NOT write on the exam sheets, there will not be room!
PLEASE show all work, writing the essential steps in the problem solution. Write appropriate
formulas first, then put in numbers. Partial credit will be LIBERAL, provided that essential work is
shown. Organized, logical, easy to follow work will receive more credit than disorganized work.
The setup (PHYSICS) of a problem will count more heavily than the math of working it out.
PLEASE write neatly. Before handing in solutions, PLEASE: a) number the pages & put the pages in
numerical order, b) put the problem solutions in numerical order, & c) clearly mark your final answers.
If I can’t read or find your answer, you can't expect me to give it the credit it deserves.
I HAVE 145 EXAMS TO GRADE!!! PLEASE HELP ME GRADE THEM
EFFICIENTLY BY FOLLOWING THESE SIMPLE INSTRUCTIONS!!!
FAILURE TO FOLLOW THEM MAY RESULT IN A LOWER GRADE!!
A 8.5’’ x 11’’ sheet with anything on it & a calculator are allowed. Problem 1 (Conceptual) IS REQUIRED!
NOTE: THE FOLLOWING IS DIFFERENT FOR THIS EXAM!! You MUST ALSO
answer Problem 2!! Then, also answer either Problem 3 or Problem 4! Answer all parts of the ones
you choose! So, a total of three (3) problems are required. Problem 1 is worth 34 points. Problems
2,3,4 are equally weighted at 33 points each.
1. REQUIRED CONCEPTUAL QUESTIONS!!! Answer briefly, in complete, grammatically
correct English sentences. I want answers which use mainly ENGLISH WORDS, NOT symbols or
equations! If you insist on using symbols, DEFINE all symbols you use! ZERO CREDIT will be
given for answers with ONLY symbols!!! Be sure to answer ALL PARTS of ALL questions!
a. State the Work-Energy Principle. In class, I stressed that this is one of Newton’s Laws of
Motion expressed in Work-Energy Language rather than Force Language. Which Newton’s
Law of Motion was I talking about?
b. State the Principle of Conservation of Mechanical Energy. In class, I stressed that this
principle is valid if and only if all forces are of a certain kind. Our book also stresses this. What
kind of forces are required for this Principle to be valid?
c. State Newton’s 2nd Law in terms of Momentum. (Note: The answer ΣF = ma will receive NO credit!).
In class, I stressed that this form of Newton’s 2nd Law is important for collision problems, but
also that it is important historically. Why did I say that it is important historically?
d. State the Law of Conservation of Momentum. In class, I stressed that this Conservation Law
results from using a combination of two of Newton’s Laws of Motion to solve a collision problem. In
class, I used those two Newton’s Laws to derive this Conservation Law. A similar derivation is
also in our book. Which two Newton’s Laws of Motion are combined in a collision problem to
give this Conservation Law?
e. State Newton’s 2nd Law for Rotational Motion. (Note: The answer
ΣF = ma will receive NO credit!).
Both start
f. See figure. Two water slides are shaped differently, but they start at
here!! 
the SAME height h. They also end at the same point at the
bottom. Two riders, Paul & Kathleen, start from rest at the same time & at the
SAME height h but on different slides. (They’re shown at different heights because it
shows them AFTER they’ve started down!) The slides are frictionless. Which rider is
traveling faster at the bottom? What Physical Principle did you use to answer this?
g. 5 Point Bonus!! In the water slide problem of part f, which rider gets to the
bottom first? WHY? (Answer in words!!)
h. 5 Point Bonus!! During our energy conservation discussion, I did a
demonstration which attempted to illustrate the answer to part f about the people
on the water slides. Briefly describe this demonstration. (If you were in class the
day I did this demonstration, you probably will be able to answer this. However, if you “cut” class
that day, as many of you often do, you probably won’t be able to answer it!)
Both
end
here!

NOTE: PROBLEM 2 IS REQUIRED!!!!!
F
2. The figure is a hollow, spherical satellite of radius R = 4.6 m & mass
M = 3,400 kg, that engineers are testing in a lab. It is a perfect hollow sphere
so it’s moment of inertia is I = (⅔)MR2. (NOTE: This obviously means that the
moment of inertia for a disk, I = (½)MR2 CANNOT & should not be used
F
here!). FOUR (4) equal sized rocket engines are arranged, 90° apart, in

a plane at the equator (at radius R) of the spherical satellite. (The figure
looks down on the plane of the engines). When fired simultaneously, the engines
exert 4 equal forces F tangent to the equator of the sphere. This causes the satellite
to rotate in the plane of the figure & gives it angular acceleration α = 5.0 rad/s2.
F
If the 4 forces F are only ones producing torques. Calculate:
a. The total (net) torque τnet exerted by the total of the 4 rocket engines. What Physical
Principle did you use to find this?
b. One of the forces F.
c. The tangential acceleration atan of a point on the equator (at radius R) of the satellite.
The satellite starts from rest. After the rockets have been firing for a time t = 12.0 s, it’s
angular velocity is ω. Calculate:
d. The angular velocity ω.
e. The (tangential) velocity v of a point on the equator (at radius R) of the satellite at t = 12.0 s.
NOTE: WORK EITHER PROBLEM 3 OR PROBLEM 4!!!!!
vC = 0, y = h
3. See figure. Use energy methods to solve this!!! NO credit will be given for force

methods! You don’t need force

vB = 7.5 m/s
components or to know the incline
y=0
angle θ to solve this! A mass m = 7 kg
vA = 0, x = ?

is initially on a frictionless incline at a

height h above horizontal, frictionless
surface (point C in the figure). It is
released from rest & moves down the
incline to the horizontal surface (point B in the figure). At that point, it’s velocity is
vB = 7.5 m/s. It continues to the left where it contacts an ideal spring, of spring constant
k = 750 N/m. It continues past that point, compressing the spring until it momentarily stops
(point A in the figure, vA= 0). At that point, the spring is compressed a distance x from it’s
equilibrium position.
a. Calculate the kinetic energy of the mass at point B.
b. Calculate the gravitational potential energy that the mass initially had at point C & the
height h at which it started. What Physical Principle did you use to answer this?
c. Calculate the elastic (spring) potential energy of the mass when it comes to rest at point A
& the distance x which the spring is compressed at that point. What Physical Principle
did you use to answer this?
d. Calculate the kinetic energy & the velocity v of the mass when it was at height y = 1.1 m
above the horizontal surface. (This point is not shown in the figure. It is above point B
& below point C in the figure).

F
NOTE: WORK EITHER PROBLEM 3 OR PROBLEM 4!!!!!
4. See figure. A bullet, mass m = 0.05 kg, traveling at speed v = 375 m/s, strikes and becomes
embedded in a block of wood, mass M = 1.8 kg, which is initially
at rest on a horizontal surface. The block-bullet combination
v = 375 m/s
then to moves to the right across the surface.
a. Calculate the momentum and the kinetic energy of the
M
m
bullet before it hits the block.
b. Calculate the momentum of the bullet-block combination as they move away from
the collision. Calculate their speed V immediately after the collision. What Physical
Principle did you use to find these?
c. Calculate the kinetic energy of the bullet-block combination immediately after the
collision. Was kinetic energy conserved? WHY? Explain (using brief, complete,
grammatically correct English sentences! Hints: PLEASE THINK before answering
this! Compare the kinetic energy found here with that found in part a! It is
PHYSICALLY IMPOSSIBLE for the kinetic energy after the collision to be larger
than the kinetic energy before the collision!).
d. Calculate the impulse Δp delivered to the block by the bullet. Stated another way,
find the change in momentum of the block due to the collision. If the collision time
was Δt = 1.8  10-3 s, calculate the average force exerted by the bullet on the block.
What Physical Principle did you use to find this force?
V=?