Exam Review #1
Dimensional Analysis
through Power
Supplemental Instruction
Iowa State University
Leader: Wesley
Course: PHYS 221
Instructor: Whisnant
Date: 02/17/2014
Practice Exam #1
Please bring this with you to the SI review
session on Monday, February 17. It will
behoove you NOT to look past this page until
then.
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu
Do NOT plug in numbers until you have solved for the desired variable!
Try to solve each problem algebraically first.
1. The figure on the right shows two vectors
A and B that lie in the x-y plane with
magnitudes A and B, respectively. Their
angles with respect to the positive x-axis
are 70 degrees and 135 degrees,
respectively. What is the magnitude of
the projection of vector B on A?
A.
B.
C.
D.
E.
F.
ABcos(65 degrees)
Bcos(135 degrees)
Bcos(65 degrees)
Bcos(205 degrees)
ABcos(205 degrees)
Dude. B is printed onto this
paper, not projected.
2. Vectors A, B, and C satisfy the vector equation A + B = C. Their magnitudes are related
by A = B = C. Which of the following is an accurate statement?
A. B and C are perpendicular vectors.
B. B and C are antiparallel vectors.
C. A, B, and C form the sides of an equilateral triangle.
D. A, B, and C form the sides of a right triangle.
E. The angle between A and B can have any value, in view of the limited information.
F. If A + B = C, then it is impossible for all of them to be equal.
Do NOT plug in numbers until you have solved for the desired variable!
Try to solve each problem algebraically first.
3. A cat spins around on a ceiling fan blade at an initial angular speed of 1.43 * 104 rad/s. It
undergoes constant angular acceleration for 2.00 s and reaches an angular speed of 4.73 *
104 rad/s before it flies off. How many revolutions does the cat make during this period?
A. 6.16 x 105
B. 2.99 x 105
C. 4.72 x 104
D. 1.65 x 104
E. 9.80 x 104
F. I love performing experiments like this at home!
4. A boat must cross a 300-m-wide river and
arrive at a point 340 m upstream from where
it starts (see figure). To do so, the pilot must
head the boat at a 60º upstream angle. The
current has a speed of 3.0 m/s. The trip across
the river takes 60 s. What is the speed of the
boat in still water, in m/s?
A. 3.0
B. 5.0
C. 7.6
D. 8.7
E. 10.0
F. This question is silly. This is what
speedometers are for.
Do NOT plug in numbers until you have solved for the desired variable!
Try to solve each problem algebraically first.
5. A ball sits at rest on a horizontal tabletop, which in turn stands on the surface of the
Earth. The weight of the table is one half of a Newton’s third law force pair. Which force
is the other half?
A. The upward force that the table’s gravity exerts on the Earth
B. The upward force that the table top exerts on the ball
C. The downward force that the ball exerts on the table
D. The downward force that the Earth’s gravity exerts on the table
E. The frictional force between the Earth and the table top
F. The tipping force that my hands will exert on the table due to my frustration with this
question
6. A man pushes a block on a horizontal table on Earth, with friction. This block accelerates
at 2.0 m/s2 when a 40 N horizontal force is applied to it. The man happens to be an
astronaut, and thinks it would be a fantastical idea to do the exact same thing on the
moon, only with a force of 80 N! The block and table are then set up on the Moon where
the acceleration due to gravity is 1.62 m/s2. What acceleration, in m/s2 does this force
impart to the block?
A. 8.0
B. 2.0
C. 4.0
D. 1.6
E. I need to know the coefficient of friction between the block and the table in order to
solve this problem.
F. … What is this man even trying to prove?
Do NOT plug in numbers until you have solved for the desired variable!
Try to solve each problem algebraically first.
7. A 300 kg roller coaster goes through a circular loop-the-loop with a radius of 100 m. At
the top of the loop, the angular velocity of the coaster is 0.5 rad/s. What is the normal
force exerted on the coaster by the track at that point?
A. 4557 N
B. 7500 N
C. 15000 N
D. 2943 N
E. 0 N
F. I’m having way too much fun riding this roller coaster to worry about this problem
right now.
8. In the figure, a girl is pulled in a box with a
noticeable mass by her big brother. Both the
girl and the box are moving as one unit. There
is a noticeable amount of friction between the
box and the ground. Air resistance is
negligible. If the box and the girl are moving
at a constant velocity, which one of the
following statements is true?
A. The horizontal force that the box exerts on the
girl points to the left.
B. The horizontal force that the box exerts on the
girl points to the right.
C. The box exerts no horizontal force on the girl.
D. The pulling force is greater than the friction force.
E. The pulling force is less than the friction force.
F. This is one of the cutest physics questions I’ve ever had the opportunity to answer.
Do NOT plug in numbers until you have solved for the desired variable!
Try to solve each problem algebraically first.
9. Now, treat the girl in the box as a single unit. Her brother has the great idea of taking her
to the top of a hill that has an incline with the horizontal at an angle of 30.0 degrees and
letting her slide down in the box. He lets the box go, and it takes the girl 5.00 seconds to
get to the bottom, traveling a distance of 20.0 m along the incline. What is the coefficient
of kinetic friction between the box and the hill?
A.
B.
C.
D.
E.
F.
0.577
0.188
0.389
1.60
It is impossible to find this without the mass of the girl and the box.
OH MY GOSH, IS HE TRYING TO KILL HER?!?!!?
Do NOT plug in numbers until you have solved for the desired variable!
Try to solve each problem algebraically first.
10. The system of blocks on a string shown here is set into motion. During this motion, block
C descends with a constant speed of 2.0 m/s for 3.0 seconds. mA = 2.0 kg, mB = 3.0 kg,
and mC = 5.0 kg, while the coefficient of kinetic friction between both the level and
inclined surface is 0.40. What is the work done by gravity on the system while the two
masses are moving? Assume that block A never reaches the incline in the 3.0 seconds.
A.
B.
C.
D.
E.
F.
883 J
589 J
294 J
188 J
-188 J
I can’t physics
hard enough to
do this
question.
11. A 0.50 kg racquet ball hits a wall with a velocity of 20 m/s and bounces back with a
velocity of 15 m/s. How much work is done on the ball, in J?
A. −44
B. –1.3
C. 0
D. +1.3
E. +44
F. Fun fact: Wesley’s mom can probably beat me in a game of racquetball.
Do NOT plug in numbers until you have solved for the desired variable!
Try to solve each problem algebraically first.
12. A runner who weighs about 70 kg runs 1 km at a constant speed of 1 m/s. During this
run, he burns about 500,000 J of energy. What is his power output while he runs this km?
A. 100 W
B. 250 W
C. 500 W
D. 1,000 W
E. 500,000 W
F. This man must have thighs of steel!
13. Wesley’s grandmother’s truck weighs about 2000 N, and its engine is rated at a power of
22 kW. If Wesley’s grandmother is driving on a level road into a strong wind at a
constant velocity of 26.8 m/s, what force is being applied to the truck via the engine if it’s
operating at full power?
A. 0.821 N
B. 821 N
C. 2000 N
D. 0 N
E. 1583 N
F. Wesley’s grandma’s truck sounds way better than my truck.