EXAM I, PHYSICS 1403, July 18, 2012, 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! This
wastes paper, but it makes my grading easier!
2. 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.
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
& 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.
5. NOTE!! The words “EXPLAIN”, “DISCUSS” & “DEFINE” below mean to answer
mostly in ENGLISH, NOT math symbols!
I HAVE 32 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 (mostly) CONCEPTUAL QUESTIONS!!!
a. Significant Figures: Multiply 4.675  107 m/s by 8.52  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! Answers
which don’t use power of 10 notation will receive ZERO CREDIT!
Answer briefly parts b., c., d & e. 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!
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. Suppose you are riding in a convertible with the top down. The car is
moving to the right (x-direction) at constant velocity v0x . You throw a ball
straight up (from your viewpoint) with an initial velocity v0y while the car travels
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. (Note: If you do not make a sketch, you will lose points!!)
d. 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!)
e. Near the beginning of the Free Fall discussion, I briefly discussed the history of the
subject. Tell me the name (either last name or first name is ok) of the person who first
did experiments showing that the acceleration due to gravity is the same for all objects,
independent of size. (Hint: The answer is not “Isaac Newton”!!).
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 traveling at velocity v0 = 50 m/s along the
positive x-axis. It undergoes a constant acceleration in the negative x
direction, so it is slowing down. After it has moved a distance x = 400
m, it has slowed to v = 28 m/s. Calculate:
a. The car’s acceleration.
b. The time it takes it to slow from 50 m/s to 28 m/s.
c. The distance past the origin that it finally stops.
d. The time after it passes the origin that it finally stops.
e. It’s velocity a time t = 15 s after it has passed the origin.
a
v0
v
t = 0, v0 = 50 m/s
x = 400 m, v = 28 m/s
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
3. See figure. A boy playing with a pellet gun stands on the ground beside a building of
height h = 40 m. He fires a pellet straight upward with an initial velocity
v0 = 32 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 (2dimensional) 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 = 40 m.
d. The time it takes the pellet to reach the building height, y = 40 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 = 2.0 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!)
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
4. See figure. A stone is thrown from the roof of a building with initial velocity
v0 = 35 m/s at an angle θ0 = 27° with the horizontal. The roof is at height
h = 50 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.
 h = 40 m

v0 = 32 m/s
y
v0
θ00
x
It is best to take the upward direction as positive! (Hint: That the stone

starts at height h = 50 m above the ground is totally irrelevant to every
|
question but part f!). Calculate:
h
=
50
m
a. The horizontal and vertical components of the initial velocity v0.
|
b. The stone’s maximum height above the top of the building.
|
c. The time the stone takes to reach the height calculated in part b.

d. The time it takes the stone to go up, come down & again reach the
height it started from (50 m above the ground; where the dashed
---- d ----
curve crosses the x-axis in the figure!). At that same position, calculate it’s
horizontal (x) distance from the starting point.
e. The horizontal & vertical components of its velocity, vx & vy, after the stone has been in
the air for 2.5 s.
f. 5 POINT BONUS! Calculate the time it takes the stone to reach the ground. Use that
result to find the horizontal distance (d) from the building where it lands. (Hint: Solving
this will require you to solve a quadratic equation using the quadratic formula!)
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) 155 km, away, in
a direction 30° North of East. Then, it flies to city B (following
displacement b) 177 km away, in a direction 20° West of North.
Finally, it flies 198 km due West, to city C (following displacement c).
The resultant displacement is R in the figure. (You DON’T need to
convert km to m to do this!). Calculate:
a. The vector components of the displacements a, b & c along the
East-West (x) axis & along the North-South (y) axis. (Caution!
Make sure that you use the correct trig function for the components of b!)
b. The components of the resultant vector R = a + b +c along the x-axis & along the y-axis.
c. The magnitude & direction (with respect to the x-axis) of the resultant displacement
vector, R, of the plane. (Use the results of part b). (Caution! Make sure that you use the
correct trig function and angle for the components of R!)
For parts d & e, assume that the plane flies horizontally at constant speed for the flight
(neglecting 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!!
The y-axis is NOT vertical here! It is parallel to the Earth’s surface, along the North-South
direction. If you think about parts d & e & use definitions, you may find that they are the
easiest questions on this exam!). Calculate:
d. The average SPEED of the plane for the trip from A to C.
e. The average VELOCITY of the plane for the trip from A to C.