EXAM I, PHYSICS 1403
February 18, 2004
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 shown. Organized, logical, easy to follow work will receive more credit
than disorganized work.
3. The setup (PHYSICS) of a problem will count more heavily than the math of working it out.
4. PLEASE write neatly. Before handing in your solutions, PLEASE: a) number the pages and
put the pages in numerical order, b) put the problem solutions in numerical order, and 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 118 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!! THANK YOU!!
A 8.5’’ x 11’’ sheet with anything on it & a calculator are allowed. Problem 1
(Conceptual Questions) 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, and 4 are equally weighted & worth 33 points each.
1. THIS PROBLEM IS REQUIRED!!! CONCEPTUAL QUESTIONS: Answer
these briefly, in a few complete and grammatically correct English sentences.
a. State Newton’s 1st Law and Newton’s 3rd Law.
b. A child sits in a wagon, which is moving to the right (xdirection) at constant velocity v0x (see figure). She throws
an apple straight up (from her viewpoint) with an initial
velocity v0y while she continues to travel forward at v0x.
Neglect air resistance. Will the apple land behind the
wagon, in front of the wagon, or in the wagon? WHY? Explain (briefly!) your
answer. (Use what you know about projectiles!). Make a sketch of the situation to
illustrate your explanation. Answer the following for a 5 POINT BONUS! During
our class discussion about projectiles, I did an in-class demonstration which
illustrates the answer to this question about the child in the wagon. 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!)
c. See figure. A hockey puck is sliding (to the right) at
constant velocity across a flat, horizontal, frictionless
ice surface. Which of the sketches in the figure is the
correct free body diagram for this puck? WHY?
Explain your answer using Newton’s Laws! (Hint: Is
there a force in the direction of the puck’s motion?)
NOTE: Answer any two (2) of problems 2, 3, & 4!!!
2. See figure. A football is punted so that
it leaves a player’s foot a distance y =
0.65 m above the ground. The ball’s
initial velocity is v0 = 20 m/s at an
angle of 0 = 37 with the horizontal.
Neglect air resistance. Use the
coordinate system in the figure (x = y = 0 where the football leaves the player’s foot)
to answer these questions.
a. Compute the horizontal and vertical components of the initial velocity.
b. What is the maximum height (above the ground) of the footba1l? How long does
it take to reach this maximum height?
c. How long does the ball take to again reach the height it started from (0.65 m
above ground level; where the dashed curve crosses the x-axis in the figure)? At
that point, what is it’s horizontal (x) distance from the kicker’s foot?
d. What are the ball’s height and horizontal displacement after it has been in the air
for 1 s?
e. What is its velocity (magnitude and direction) after it has been in the air for 1 s?
(Alternatively, what are the horizontal and vertical components of velocity after
it has been in the air for 1 s?)
f. 5 POINT BONUS! How long does it take to reach the ground? When it does so,
what is its horizontal distance from its starting point? (Hint: You will need to use
the quadratic equation to answer this question!)
v0 
3. See figure. A box, mass m = 30 kg, is given a shove across a horizontal
surface. It is released at the origin with an initial velocity of v0 = 15
m/s in the +x-direction. After it is released, the only horizontal force
on the box is friction between it and the surface, which causes it to
slow down and eventually come to rest. The coefficient of kinetic
friction between the box and the surface is k = 0.30.
a. Draw the free body diagram for the box, properly labeling all forces. Is there a
force in the direction of the motion (parallel to the velocity)?
b. Compute the weight of the box and the normal force between it and the surface.
c. Compute the frictional force the box experiences as it slides across the surface.
What is the direction of this force?
d. Write the equation which results from applying Newton’s 2nd Law for the box’s
motion in the x-direction. Use this equation to compute the acceleration
(magnitude and direction) of the box as it slows down. What force causes this
acceleration?
e. How far from the origin will the box go before coming to rest? How long will it
take to stop?
f. Compute its velocity and its distance from the origin a time t = 2s after
it is released.
NOTE: Answer any two (2) of problems 2, 3, & 4!!!
4. See figure. Two masses (m1 = 20 kg and m2 = 30 kg) are connected by a massless
cord and placed on a horizontal, frictionless surface. The two-mass system is
accelerated to the right by a force FP = 50 N using a cord attached to m1
that makes an angle  = 30with the
horizontal. There is no vertical
motion.
a. Let the tension in the cord connecting the two masses be FT, and draw the free
body diagrams for the two masses, properly labeling all forces.
b. Compute the horizontal and vertical components of the applied force FP.
c. Write the equations which result from applying Newton’s 2nd Law to both m1 and
m2 in both the horizontal (x) and the vertical (y) directions. You will receive
more credit by writing these in terms of symbols, without numbers substituted in,
than you will by writing them with numbers substituted in!
d. Compute the normal force between mass m1 and the horizontal surface. Is this
normal force equal (and oppositely directed) to the weight m1g? If so, why? If not
why not? Justify your answer using the appropriate Newton’s 2nd Law equation
from part c.
e. Using the appropriate Newton’s 2nd Law equations from part c., compute the
acceleration a of the system and the tension FT in the cord connecting the two
masses. (Hint: If part c has been done correctly, getting the answers to this part
will require you to simultaneously solve two linear algebraic equations with two
unknowns: FT and a.)