EXAM I, PHYSICS 1306
July 17, 2002
Dr. Charles W. Myles
INSTRUCTIONS: Please read ALL of these before doing anything else!!!
1. PLEASE put your name and social security number on every sheet of paper you use.
2. PLEASE write on one side of the paper only!!
3. PLEASE do not write on the exam sheets, there will not be room! If you don’t have
paper, I will give you some.
4. PLEASE show all of your work, writing down at least the essential steps in the
solution of a problem. Write down the appropriate formulas first, then put in the
numbers. Partial credit will be LIBERAL, provided that the essential work is shown.
Organized work, in a logical, easy to follow order will receive more credit than
disorganized work.
5. NOTE!!! The setup (THE PHYSICS) of a problem will count more heavily in the
grading than the detailed mathematics of working it out.
6. PLEASE clearly mark your final answers and write neatly. If I can’t read or find
your answer, you can't expect me to give it the credit it deserves.
7. You will lose credit if you don’t show the units of an answer or if the units are wrong.
PLEASE FOLLOW THESE SIMPLE DIRECTIONS!! THANK YOU!!
An 8.5’’ x 11’’ piece of paper with anything written on it and a calculator are allowed.
NOTE: Problem 1 consists of Conceptual Questions and IS REQUIRED! You may
work any three (3) of the remaining four problems for four (4) problems total for this
exam. Each problem is equally weighted and worth 25 points, for a total of 100 points on
this exam.
1. THIS PROBLEM IS MANDATORY!!! CONCEPTUAL QUESTIONS: Answer
these briefly in a few complete and grammatically correct English sentences.
a. By using a ball thrown straight up into the air as an example, explain the error in
the common misconception that acceleration and 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.
c. A child sits upright in a wagon, which is moving to the right (the x-direction) at
constant velocity v0x (see the diagram). She throws an
apple straight up (from her point of view) 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? Explain (in brief, grammatically correct, English sentences!) your
answer. (Use what you know about projectile motion!). Make a sketch of the
situation to illustrate your explanation.
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
2. A car is initially at the origin and is initially traveling at a constant speed of 30 m/s
along the positive x-axis. See figure. At time t = 0 the driver sees an object in the
road and applies the brakes. His reaction time is 0.6 s. The reaction time is the time
between his seeing the object and applying the brakes. During the reaction time, the
velocity is constant.
a. How far does the car travel during
this reaction time?
After this 0.6 s have passed, the brakes are applied and this causes the car to slow
down at a constant acceleration of –4.0 m/s2.
b. What distance does the car go between the time the brakes are applied until it
stops?
c. How long after the brakes are applied does it take the car to stop?
d. What is the car’s velocity 4 s after the brakes are applied?
e. How far has the car moved after the brakes have been applied for 6 s?
3. A person throws a ball upward into the air with an initial velocity of 15 m/s. It goes
up and eventually comes back down. See the figure. Assume vertical motion
only and neglect air resistance in what follows.
a. What are the ball’s acceleration and velocity at the top of its flight?
b. What is the maximum height the ball reaches?
c. How long does it take the ball to get to its maximum height? How long does
it take the ball to make one complete round trip and come back to the
person’s hand?
d. What is the ball’s velocity (magnitude and direction) when it reaches the
person’s hand again?
e. At what times does the ball pass a point 8 m above the ground?
NOTE: WORK ANY THREE (3) OF PROBLEMS 2., 3., 4., or 5.!!!!!
4. On the Klingon home planet, the acceleration due to gravity is g = 6.0 m/s2.
(Note: This means DO NOT use g = 9.8 m/s2 in what follows!!).
A Klingon shoots a cannon ball at ground level towards a
target. The initial velocity of the cannonball is v0 = 140 m/s
at an angle of 0 = 35 with the horizontal. See
figure. Neglect air resistance.
a. What are the horizontal and vertical components of the
initial velocity?
b. What is the maximum height of the cannonball? How long does it take to reach
this height?
c. How long does it take to hit the ground? When it does so, what is its horizontal
distance from its starting point?
d. What are its height and horizontal displacement after it has been in the air for
10 s?
e. What is its velocity (magnitude and direction) after it has been in the air for 10 s?
(Alternatively, what are its horizontal and vertical components of velocity after it
has been in the air for 10 s?)
5. An airplane is heading due West at a constant speed, with respect to still air, of
275 km/h. A strong wind begins blowing from the Northeast (towards the
Southwest) at a constant speed of 50 km/h. See the figure. NOTE: You do NOT need
to convert km/h to m/s to do this problem! Use the analytic (trigonometric) method to
do the required vector addition in what follows, NOT the graphical method.
a. Make a sketch of the situation and label it with appropriate quantities.
b. What is the resultant velocity (magnitude and direction) of the airplane with
respect to the ground?
c. What is the component of this velocity along the East-West axis? What is the
component of this velocity along the North-South axis?
d. After the wind has been blowing for 0.5 hour, if the pilot has taken no corrective
action, what is the component of the airplane’s displacement along the East-West
axis? What is the component of this displacement along the North-South axis?
e. What are the magnitude and direction of the total displacement of the airplane 0.5
hour after the wind starts blowing (if the pilot takes no corrective action)?