EXAM I, PHYSICS 1403
September 30, 2008, Dr. Charles W. Myles
INSTRUCTIONS: Please read ALL of these before doing anything else!!!
1. 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!
2. 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
3.
4.
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 your 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.
NOTE!!! I HAVE 180 EXAMS TO GRADE!!! PLEASE
HELP ME GRADE THEM EFFICIENTLY BY FOLLOWING THE
ABOVE SIMPLE INSTRUCTIONS!!! FAILURE TO FOLLOW
THEM MAY RESULT IN A LOWER GRADE!! THANKS!!
A 8.5’’ x 11’’ sheet with anything on it & a calculator are allowed . Problem 1 (Conceptual) IS
REQUIRED! Answer any two (2) of the remaining problems for a total of three (3) problems
required. Problem 1 is worth 34 points. Problems 2, 3, & 4 are equally weighted & worth 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! For parts a & b:
Newton’s Laws are about forces. Complete statements of each Law MUST mention forces!
If a part contains more than one question, please be sure to answer each one!
a. State Newton’s 1st Law. How many objects at a time does it apply to?
b. State Newton’s 3rd Law. How many objects at a time does it apply to?
c. See figure! Suppose that you are riding in a convertible with the top down. It
is moving to the right (x-direction) at constant velocity v0x. You throw a
ball straight up (from your viewpoint) with initial velocity v0y while the car
moves forward at v0x. Neglect air resistance. Will the ball land behind the
car, in front of the car, or in the car? WHY? Explain (briefly!) your answer. Use what you
know about projectiles! Make a sketch of the situation to illustrate your explanation.
d. See figure. A box is sliding at constant velocity (v = constant!) across
v
a flat, horizontal, frictionless surface. Sketch the free body (force)
diagram for this box. Is there a force in the direction of the box’s
motion? Explain your answer using Newton’s Laws! Caution! To
answer this correctly, you must think like Newton (of about 400 years
ago) NOT like Aristotle (of about 4,000 years ago)! NOTE: Velocity is
NOT a force & doesn’t belong in a free body diagram.
e. Answer the following for 5 POINT BONUS! During our projectile discussion, I did an
in-class demonstration which tried to illustrate the answer to question c, about the car
and the ball. Briefly describe this demonstration. If you were in class when I did it, you
should be able to answer this. If you “cut” class that day, as many of you often do, you
probably won’t be able to answer it!
NOTE: Answer ANY TWO (2) of problems 2, 3, & 4!!!
2.
See figure. A person throws a stone from the top of a building with initial velocity v0 = 30
y
m/s at an angle θ0 = 35° with the horizontal. When it is thrown, it’s a distance h = 45 m
above the ground. Neglect air resistance. Use the coordinate system in the figure (x = y = 0
where the stone leaves the person’s hand) to answer these questions. It is best to take the upward
direction as positive! (Hint: That the stone starts 45 m above the ground is totally

irrelevant to every question but part e!)
a. Calculate the horizontal & vertical components of the initial velocity.
b. Calculate the stone’s maximum height above the top of the building.
Calculate the time the stone takes to reach this height.
c. Calculate the time it takes to go up, come down & again reach the height it
v0
θ0
x
|
h = 45 m
|
|

started from (45 m above the ground; where the dashed curve crosses the x-axis in the figure!).
---- d ----
At that same position, calculate it’s horizontal (x) distance from the starting point.
d. Calculate the horizontal & vertical components of it’s velocity, vx & vy, after the stone has been in
the air for 2.5 s. Calculate the stone’s velocity (magnitude or length and direction) after it has been in
the air for this same time.
e. 5 POINT BONUS! Calculate the time it takes the stone to reach the ground. Calculate the
horizontal distance (d) from the building where it lands. (Hint: You will need to use the quadratic
formula to answer this!).
3.
See figure. A helicopter, mass M = 7750 kg, moves up with acceleration a. It lifts an object, mass m =
1025 kg, which is connected to it’s bottom by a massless cable. The upward force on the
helicopter exerted by the air on the rotors is FP = 1.1  105 N. The cable tension, FT, of course,

acts down on the helicopter & up on the object. The acceleration a & the tension FT are

unknown.
FP
a. Sketch the free body diagrams for the helicopter & for the object, properly
labeling all forces. Don’t forget the weights of the helicopter & the object,
which aren’t shown in the figure!
 a
b. Apply Newton’s 2nd Law to the copter & the object to find 2 equations
 FT
needed to solve for a & FT. Writing these without substituting in numbers,
copter
will receive more credit than writing them with numbers in them!
M = 7750 kg
 FT
c. Using the equations derived in part b, calculate a & FT. (Hint: This
requires you to do the algebra to solve 2 simultaneous linear equations in 2
unknowns!)
load
m = 1025 kg
d. When the cable becomes tight & the copter starts to lift the object, it
is moving up at velocity v0 = 8 m/s. Calculate the distance it has traveled a time t = 6.0 s later.
4.
See figure. A box, mass m = 15 kg is connected to a massless cord & placed on a horizontal table. It
is pulled to the right by a force FP = 50 N that makes an angle  = 35° with the horizontal.
a
There is no vertical motion. The coefficient of kinetic friction between the mass & the
table is μk = 0.25.
a. Sketch the free body diagram for the box, properly labeling all forces.
m
b. Calculate the horizontal (x) & vertical (y) components of the applied force FP.
nd
c. Write the two equations which result from applying Newton’s 2 Law to the box
in the horizontal (x) & vertical (y) directions. You’ll receive more credit by writing these with
symbols, without numbers substituted in, than you will by writing them with numbers in them!
d. Calculate the normal force FN between box & the table. Is this force equal (and oppositely directed)
to the weight mg? If so, why? If not why not? Justify your answer using the appropriate Newton’s
2nd Law equation from part c. Calculate the frictional force, Ffr between the box & the table.
e. Using the appropriate Newton’s 2nd Law equation from part c., calculate the acceleration a of the
box. What forces cause this acceleration?
θ
FP
Ff