Download Coefficient of Rolling Friction - General Physics - Solved Past Paper and more Exams Physics in PDF only on Docsity! First Name: Last Name: Section: a1
March 26, 2008 Physics 207
EXAM 2
Please print your name and section number (or TA’s name) clearly on all pages. Show all
your work in the space immediately below each problem. Your final answer must be placed in the
boxes provided. Problems will be graded on reasoning and intermediate steps as well as on the final
answer. Be sure to include units wherever necessary, and the direction of vectors. Each problem is
worth 20 points. Try to be neat! Check your answers to see that they have the correct dimensions
(units) and are the right order of magnitude. You are allowed one sheet of notes (8.5” x 11”, 2 sides),
acalculator, and the constants in this exam booklet. The exam lasts exactly 90 minutes.
Constants:
Acceleration due to gravity at the earth’s surface: g = 9.81] mis’
Ss 2 Luv oVS
ee
SCORE:
Problem 1:
Problem 2:
Problem 3:
Problem 4:
Problem 5:
TOTAL:
Don't open the exam until you are instructed to start.
“| have no special talent. | am only passionately curious.” A. Einstein
First Name: Last Name: Section: g2
Problem 1
a.) A 1000 kg car climbs a 5.0° slope at a constant velocity of 80.0 kiv/h. Assuming that air resistance
may be neglected, at what rate must the engine deliver energy to the drive wheels of the car? Express
your answer in kW.
“2
P= 4¥ = “4 e - meee
3
30,0N10 1
= 1000 %4.3% oe | sin
2,08
= 20 ew
b.) Truck brakes can fail if they get too hot. In some mountainous areas, ramps of loose gravel are
constructed to stop runaway trucks that have lost their brakes. The combination of a slight upward
slope and a large coefficient of rolling friction as the truck tires sink into the gravel brings the truck
safely to a halt. Suppose a gravel ramp slopes upward at 6.0° and the coefficient of rolling friction is
0.40. Use work and energy to find the length of a ramp that will stop a 15,000 kg truck that enters the
ramp at 35 m/s (about 75 mph).
fk
wo =
tu a
35
Le Uw
ag (sine +a 62 ©) : 245 ( Mn Us 0-9 tok
fy
120 m
First Name: Last Name: Section:
d.) What is the torque (magnitude and direction) on the flywheel? (4 pts)
TT v
K —_——
x
Lb wT _ ow rem
In Pays
br Vw)
e.) Find the work done by the force on the flywheel (make sure to indicate whether the work is
positive or negative) (4 pts.) an j
OE ae mh
FirstName: Last Name: Section: a6
Problem 4
Timbie and Chung want to determine whose car is more massive. They are advised by Physics 207
students to find out the answer by colliding the cars together.
In experiment 1, Timbie’s car, with mass mr, is at rest when Chung’s car, mc crashes into it with
initial velocity v;. After the impact the two cars remain locked together and move with velocity vp.
In experiment 2, the cars are pulled apart from each other and collided again, this time with Chung’s
car at rest and Timbie’s crashing into it with the same initial velocity, v;, as in experiment 1. The cars
remain locked together after the impact and this time move with velocity v¢'.
a.) In experiment 1, what is the ratio of the final kinetic energy to the initial kinetic energy? Express
your answer in terms of mr and mc. (7 pts)
’ mer = (meme) YE
KE ¥ wy +m) Ue ;
t ( 6 1) f WwW MemMt ay
——— = — eof aa OY
LE; x Me ar — a a We
=
;
| S
REL me
YE; ~ Mer)
b.) Using the results of both experiments, what is the mass of mr in terms of mc, vg and vy? (7pts)
Sow cod Lav onl
thee é
i
Gite maa(momy
?
Get \ = Cm tm.) ?
(ea wtlag wt ry =
w
wr vA ’
. Mee [Me “hy,
First Name: Last Name: Section: w7
Now for a different problem:
c.) A 1.6 kg particle moving along the x-axis experiences the net force shown in the figure. The
particle's velocity is 4.0 m/s in the positive x direction at x = 0 m. What is its velocity at x = 2 m? (6
pts) Zz
FN) Wwe AY= ( Fx) de
Ws. D
N\ zu
mone = Vo) dk
—10 NY 2
z
2
on 2
od
2Ze-/D= 10 >
W
hyo 2 WI od
Parride ic asalontd. Fy cm Us} 3 Jz
be gue <3
4.0
z Ie
ng - 4 1 bt4.0 a) -
—_——
Tyhb
ZI