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EXAM I, PHYSICS 1408, July 15, 2009, 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 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!! The words “EXPLAIN”, “DISCUSS” & “DEFINE” below mean to answer
mostly in ENGLISH, NOT math symbols!
NOTE: I HAVE 38 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!!
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. Each problem is equally weighted & worth
25 points, for 100 points on this exam.
1. MANDATORY (mostly) CONCEPTUAL QUESTIONS!!! Answer briefly parts a., b., c.
& d. in a few 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! NO credit will be given for answers with ONLY symbols!
a. Using a ball thrown straight up into the air as an example, explain the error in the
common misconception that acceleration & velocity are always in the same direction.
b. Explain the error in the common misconception that an object thrown upward
has zero acceleration at its highest point. (What would happen if that were true?)
c. See figure! A child sits in a wagon moving to the right (x-direction) at constant
velocity v0x. 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.
d. For 5 BONUS POINTS, answer the following: Yesterday, I did an in-class
demonstration to try to illustrate a similar situation to that in part c about the girl, the
wagon, & the apple. Briefly describe this demonstration. (If you there when I did this
demonstration, you’ll probably be able to answer this. But, if you “cut” class that day, as
several of you are already in the habit of doing, you probably won’t be able to answer it!)
e. Significant Figures: Divide 4.634  107 m/s by 8.6  10-3 s. Assuming that all digits in
both of these numbers are significant, write the answer with the correct number of
significant figures. Express your answer using scientific (power of 10) notation!
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
2. See figure. At time t = 0, a car is at the origin & is
t=0
traveling at velocity v0 = 45 m/s along the positive xv0 = 45 m/s
axis. It undergoes a constant acceleration in the
x = 450 m
negative x direction, so it is slowing down. After it
v = 25 m/s
has moved a distance x = 450 m, it has slowed to v =
25 m/s.
a. Calculate the car’s acceleration.
b. Calculate the time it takes it to slow from 45 m/s to 25 m/s.
c. Calculate the distance past the origin that it finally stops.
d. Calculate the time after it passes the origin that it finally stops.
e. Calculate it’s velocity a time t = 10 s after it has passed the origin.
a
v0
v
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
3. See figure. A stone is thrown straight upward from the top of a
building of height h = 65 m, with an initial velocity v0 = 35 m/s. The
stone just misses the edge of the roof on it’s way down, 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 at
the top of the building; this would mean that y = - 65 m at the ground
level. The fact that the building is 65 m high is TOTALLY IRRELEVANT
to every question but part e!]. Neglect air resistance in the following.
v0 
= 35 m/s
a. Calculate the time it takes the stone to reach it’s maximum height.
b. Calculate the time it takes it to return to the same height from
h
which it started, at the top of the building.
= 65 m
c. Calculate maximum height (above the top of the building) that the
stone reaches.
d. Calculate stone’s velocity (including direction) when it reaches
the same height from which it started, at the top of the building.
e. Calculate the stone’s height ABOVE THE GROUND at a time
t = 8.0 s after it is thrown. (Hint: The height above the ground is NOT the same as y,
which measures displacement from the top of the building!)
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
4. See figure. A cannon ball is shot from the ground with an initial velocity v0 = 40 m/s
at an angle θ0 = 43° with the horizontal. It lands on top of a nearby building of height
h = 35 m above the ground. Neglect air resistance. To answer these questions, take x0
= y0 = 0 where the cannon ball is shot. It is probably best to take the upward direction
as positive! (Hint: That the building’s height is 35 m above the ground is TOTALLY
IRRELEVANT to every question but that in part e!)
Neglect air resistance in the following.
a. Calculate the horizontal & vertical
components of the initial velocity.
h
b. Calculate the cannon ball’s maximum height
above the ground. Calculate the time it takes
θ0
to reach this maximum height.
c. Calculate it’s horizontal (x) distance from the
-------------------- d ----------------------
starting point when it has reached it’s
maximum height.
d. Calculate the horizontal & vertical components of velocity, vx & vy, after the
cannon ball has been in the air for a time t = 3.0 s. Calculate the 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 cannon ball to land on the top
of the building. When it does so, calculate it’s horizontal distance d from its
starting point. (Hint: You will need to use the quadratic equation to answer this!).
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
5. See figure. A plane starts at the origin & takes the route shown. It
first flies to city A (following displacement a in the figure) 180 km,
away, in a direction 30° North of East. Then, it flies to city B
(following displacement b) 157 km away, in a direction 20° West of
North. Finally, it flies 192 km due West, to city C (following
displacement c). The resultant displacement is R in the figure. (Hint:
You DO NOT need to convert km to m to do this!)
a. Calculate the vector components of the displacement vectors a, b & c along the
East-West (x) axis & along the North-South (y) axis. (That is, calculate the x & y
components of the three displacement vectors.)
b. Calculate the x & y components of the resultant displacement vector R = a + b +c.
c. Use the results of part b to calculate the magnitude & direction (with respect to the
x-axis) of the resultant displacement vector, R, of the plane.
For parts d & e, assume that the plane flies horizontally at constant speed for the
flight (neglect take off & landing times & neglecting the effects of wind ). The complete
flight takes a time t = 3.7 h. (Hints: Moving horizontally at constant speed means that
there is NO ACCELERATION! The acceleration due to gravity g is TOTALLY
IRRELEVANT to this problem!! If you think about parts d & e & use definitions, you may
find that they are the easiest questions on this exam!)
d. Calculate the average SPEED of the plane for the trip from A to C.
e. Calculate the average VELOCITY of the plane for the trip from A to C.