EXAM I, PHYSICS 1403
October 6, 2006
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 130 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!! THANKS!!
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. REQUIRED PROBLEM!!! CONCEPTUAL QUESTIONS: Answer these briefly,
in a few complete and grammatically correct English sentences.
a. State Newton’s 1st Law. How many objects at a time does it apply to? State
Newton’s 3rd Law. How many objects at a time does it apply to?
b. See figure. A child sits in a wagon, which is moving to the right (xdirection) 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.
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?) To answer
this correctly, you need to think like Newton (of more
than 300 years ago) NOT like Aristotle (of more than 3,000 years ago)!
d. Answer the following for a 5 POINT BONUS! During our class discussion about
projectiles, I did an in-class demonstration which tried to illustrate the answer to question
b, about the person in the convertible. Briefly describe this demonstration. If you were in
class when I did it, you should be able to answer this. If you “cut” class that day, as many
of you often do, you probably won’t be able to answer it!
NOTE: Answer any two (2) of problems 2, 3, & 4!!!
2. See figure. A person throws a stone from the top of a building with an initial
velocity v0 = 30 m/s at an angle θ0 = 30° with the horizontal. When it is thrown, it
is at a distance h = 55 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 questions. It is best to take the upward direction as positive! (Hint:
That the stone starts 55 m above the ground is totally irrelevant to every question but
part e!)
h
a. Compute the horizontal & vertical components of the initial velocity.
b. Compute the stone’s maximum height above the top of the building.
------- d --------
Compute the time the stone takes to reach this height.
c. Compute the time it takes to go up, come down & again reach the height it started from
(55 m above the ground; where the dashed curve crosses the x-axis in the figure!). At that same
position, compute it’s horizontal (x) distance from the starting point.
d. Compute the horizontal & vertical components of velocity, vx & vy, after the stone has
been in the air for 3 s. Compute the stone’s velocity (magnitude or length and direction)
after it has been in the air for this same time.
e. 5 POINT BONUS! Compute the time it takes the stone to reach the ground. When it does
so, compute it’s horizontal distance d from its starting point. (Hint: You will need to use the
quadratic equation to answer this!).
3. See figure. A stock clerk pushes on a carton on a dolly. He pushes
with a force F = 70 N which makes an angle θ = 35° below the
horizontal. The mass (carton + dolly) is m = 12 kg. There is a frictional
force Ff between the dolly & the floor, acting in the opposite direction
θ
of the motion. The coefficient of kinetic friction between the box &
F
F
f
the floor is μk = 0.17. To solve this, use the x & y axes shown.
a. Sketch the free body diagram of the carton + dolly, properly
labeling all forces. Don’t forget the weight & the normal force, not shown in the figure!
Compute the x & y components of the pushing force F.
b. Compute the weight of the carton plus dolly & the normal force FN the floor exerts on
them. Is this normal force equal (& oppositely directed) to the weight? If so, why? If not,
why not? Justify your answer using Newton’s 2nd Law in the direction perpendicular to
the floor.
c. Compute the frictional force Ff that the dolly experiences as it moves to the right.
d. Use Newton’s 2nd Law to find the acceleration a experienced by the carton plus dolly.
What forces cause this acceleration?
4. See figure. Two masses (m1 = 13 kg, m2 = 18 kg) are
a = 2.5 m/s2 
connected by a massless cord and
FT
placed on a horizontal, frictionless
 
surface. The system is pulled to the
right by an unknown force FP with a
horizontal cord. This causes the masses to have an acceleration a = 2.5 m/s2 to the right.
a. Sketch the free body diagrams for the two masses, properly labeling all forces. Don’t
forget the weights & the normal forces, not shown in the figure!
b. The two unknowns in this problem are the pulling force FP and the tension, FT, in the
cord between the masses. By applying Newton’s 2nd Law to the two masses, find the two
equations needed to solve for FP & FT. Writing these equations in symbols, without
substituting in numbers, will receive more credit than writing them with numbers
substituted in!
c. Using the equations from part b, calculate FT and FP.
d. If m1 starts from rest, compute the distance it has traveled after t = 1.5 s.
a 