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EXAM I, PHYSICS 1403, July 15, 2015, Dr. Charles W. Myles
INSTRUCTIONS: Please read ALL of these before doing anything else!!!
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! This wastes paper,
but it makes my grading easier!
PLEASE show all work, writing the essential steps in the solutions. Write formulas first, then put
in numbers. Partial credit will be LIBERAL, provided that essential work is show n. Organized,
logical, easy to follow work will receive more credit than disorganized work.
The setup (PHYSICS) of a problem will count more 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!! The words “EXPLAIN”, “DISCUSS” & “DEFINE” below mean to answer mostly in
ENGLISH, NOT math symbols!
I HAVE 43 EXAMS TO GRADE!! PLEASE HELP ME GRADE THEM
EFFICIENTLY BY FOLLOWING THESE SIMPLE INSTRUCTIONS!!! FAILURE
TO FOLLOW THEM MAY RESULT IN A LOWER GRADE!! THANKS!
An 8.5’’ x 11’’ piece of paper with anything written on it & a calculator are allowed. NOTE: Question
1, Conceptual Questions IS REQUIRED! You may work any three (3) of the remaining 4 problems for
four (4) problems total. (This means 4 complete problems, with all of their parts!). Each problem is
equally weighted & worth 25 points, for 100 points on this exam.
1. MANDATORY CONCEPTUAL QUESTIONS!!! Answer each of these briefly in a few complete,
grammatically correct English sentences. If a part contains more than one question, please be sure to
answer each one! Give answers which use mainly ENGLISH WORDS, NOT symbols or equations!
If you insist on using symbols, DEFINE all symbols you use! NO credit will be given for answers
with ONLY symbols! For parts b & c: Newton’s Laws are about forces. Complete statements of
each Law MUST mention forces!
a. Briefly state THE THEME OF THE COURSE. (Note: I’ve stated this several times in class,
beginning at our first meeting! It’s also on the webpage & in some downloadable lectures!)
b. State Newton’s 1st Law. How many objects at a time does it apply to?
c. State Newton’s 3rd Law. How many objects at a time does it apply to?
Fig. 1
d. See Fig. 1. A hockey puck slides (to the right) at constant velocity v 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?) To answer correctly, you need to think like Newton (300+ years ago)
NOT like Aristotle (3,000+ years ago)!
Parts e and f are questions are about a box of mass m, under two different conditions.
In both cases, it sits statically (not moving!) on a flat horizontal table.
e. Fig. 2 is the box’s free body diagram when the only forces acting on it are the normal force
f.
FN from the table acting upward & it’s weight mg downward. Is the normal force FN in this
case equal in magnitude & opposite in direction to the weight? Why or why not? Which
Newton’s Law of Motion did you use to answer this?
Fig. 3 is the box’s free body diagram when, in addition to the normal force FN & the weight
mg, an additional downward force FP = 40 N acts on it when someone pushes on the top. Is
FN in this case equal in magnitude & opposite in direction to the weight? Why or why not?
Which Newton’s Law of Motion did you use to answer this?
Fig. 2
Fig. 3
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
2. See Fig. 4. At time t = 0, a car is at the origin & is traveling at a
velocity of v0 = 40 m/s along the positive x-axis. It
t=0
undergoes a constant acceleration a in the negative xv0 = 40 m/s
direction, so it is slowing down. At t = 15 s after it
t = 15 s
v = 20 m/s
has passed the origin, it has slowed to v = 20 m/s.
a=?
a. Calculate the car’s acceleration a.
b. Calculate the distance the car moved in the 15 s.
c. Assuming constant a, calculate the car’s velocity at time t = 20 s after it has passed the
origin.
d. Assuming constant a, calculate the distance past the origin that the car stops.
e. If the car’s mass is m = 2,000 kg, calculate the total force required to be applied to it to
slow it down & eventually stop it. What Physical Principle (or Law) did you use to do
this calculation?
Fig. 4
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
3. See Fig. 5. A boy playing with a pellet gun stands on the ground beside a
building of height h = 50 m. He fires a pellet straight upward with an initial
velocity v0 = 40 m/s. The pellet just misses the edge of the roof on its way up,
moves higher than the building and eventually falls onto the edge of the roof and
stops, as shown. [Hints: This problem deals with free fall (1-dimensional) motion,
NOT projectile (2-dimensional) motion. It’s probably simplest to take y = 0 on the
ground beside the boy.] Neglect air resistance in the following. Calculate:
a. The time it takes the pellet to reach its maximum height above the ground.
b. The maximum height above the ground that the pellet reaches.
c. The pellet’s velocity on its way up when it reaches the building height, y = 50 m.
d. The time it takes the pellet to reach the building height, y = 50 m on its way
up. (Hint: It’s easiest to do this using the results of part c!)
e. The pellet’s velocity and height above the ground at time t = 1.8 s after it is shot.
f. 5 BONUS POINTS!! Calculate the time it takes the pellet to land on the building roof.
(Hint: Solving this will require you to solve a quadratic equation using the quadratic
formula!)
\
 y = 50 m
Fig. 5

v0 = 40 m/s
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
4. See Fig 6. Two boxes are connected by a
lightweight (massless!) cord. They are
F
FT
mB = 15 kg
mA = 12 kg
resting on a smooth (frictionless!) table. The
box masses are mA = 12 kg & mB = 15 kg. A
FP = 50 N
horizontal force FP = 50 N is applied to mA.
In what follows. Let the tension in the cord
between the two masses be FT. The masses are accelerating to the right with acceleration a.
a. Sketch the free body (force) diagrams for the 2 masses, properly labeling all forces. NOTE! If
you don’t make sketches, you will lose points!
b. The two unknowns are the acceleration a & the tension in the cord between the masses FT. By
applying Newton’s 2nd Law to the two masses, find the two equations needed to solve for a &
FT. (Note: I don’t mean to just write them abstractly as ∑F = ma. I mean to write the explicit
equations which result when Newton’s 2nd Law is APPLIED to this problem! For each, I want
to see which forces are on the left side of ∑F = ma!) More credit will be given if you leave these
equations in terms of symbols with no numbers substituted than if you substitute numbers into them.
c. Using the equations from part b, Calculate: a & FT (in any order). (Note: To solve this you
MUST solve two algebraic equations in two unknowns! Attempts to find the answers without
doing this algebra will not be successful and will be given ZERO credit!)
If the two masses start from rest (v0 = 0), after time t = 5 s, Calculate:
d. Their velocity at that time.
e. The distance they have moved at that time.
Fig. 7
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
5. See Fig 7. A woman, mass m = 60 kg, (weight mg = 588 N) stands on a scale in an
elevator. (Why she brings a scale into an elevator is not explained!). There are two vertical
forces on her. These are her weight mg downward and the normal force FN exerted
upward on her body by the scale. Her free body (force) diagram is shown in the figure.
a. Which Newton’s Law of Motion tells us that the scale reading (her measured
weight or the downward force she exerts on the scale) is numerically equal to the
upward normal force FN produced by the scale on the woman? (That Law also
tells us that the directions of these two forces are equal and opposite).
Calculate the normal force FN produced by the scale on the woman (that is
calculate her measured or effective weight) under the following conditions:
b. The elevator is at rest (so that the acceleration in the figure is a = 0).
c. The elevator is moving downward with a constant velocity v = 2.0 m/s. (Hint: what is the
acceleration a in this case?)
d. The elevator is accelerating downward (as in the figure) with acceleration a = 0.25g (= 2.45 m/s2).
e. The elevator is accelerating upward (not shown in the figure) with acceleration a = 0.25g (= 2.45 m/s2).
f. Which Newton’s Law of Motion did you use to do the calculations in parts b, c, d and e?
g. 5 BONUS POINTS!! Calculate the normal force FN produced by the scale on the woman in the
disastrous case where the elevator cable has broken so that the woman, the scale and the elevator
are all in Free Fall and accelerating downward with acceleration a = g!! That is, calculate her
measured or effective weight under these conditions. (Assume that she would be able to stand on
the scale for a few seconds before she crashed to the bottom!). Write a few English sentences
concerning the physical interpretation of the value of the normal force you calculated in this case.
Fig. 6