ame: ________________________ Class: ___________________ Date: __________
ID: A
Exam 2--PHYS 101-Fall 2009
Multiple Choice
Identify the choice that best completes the statement or answers the question.
____
1. Consider this figure of a roller coaster:
At which of these points is the speed of the car the greatest?
____
____
____
a. A
c. C
b. B
d. D
2. You drop a ball from a certain height. Which of these statements describe the changes in gravitational
potential and kinetic energy as the ball falls to the ground? (KE=kinetic energy, PE=gravitational potential
energy)
a. KE is decreasing and PE is increasing
c. both PE and KE are decreasing
b. KE is increasing and PE is decreasing
d. both PE and KE are increasing
3. Two stones, one twice the mass of the other, are dropped from a cliff. Just before hitting the ground, what is
the kinetic energy of the heavy stone compared to the light one?
a. quarter as much
b. half as much
c. the same
4. Which of these statements is true?
d.
e.
a.
____
twice as much
four times as much
energy is a scalar quantity; momentum is c. both energy and momentum are scalar
a vector quantity
quantities
b. energy is a vector quantity; momentum is d. both energy and momentum are vector
a scalar quantity
quantities
5. If the momentum of an object is tripled, its kinetic energy will change by what factor? (Assume the mass of
the object is unchanged.)
a.
b.
c.
d.
zero
one-third
nine
three
1
ame: ________________________
____
____
6. A system of particles has a momentum of zero. Which of these statements is true about the kinetic energy of
the system?
a. the kinetic energy is zero
c. the kinetic energy is negative
b. the kinetic energy is positive
d. there is not enough information
7. A bouncy rubber ball and bean bag, each with the same mass, fall to the floor from the same height. Which
of these statements about the force imparted to the floor is true?
a.
____
____
ID: A
the rubber ball imparts a greater force
c.
the ball and bean bag impart the same
force
there is not enough information
b. the bean bag imparts a greater force
d.
8. In elastic collisions
a. only energy is conserved
c. only momentum is conserved
b. both energy and momentum are
d. none of these
conserved
9. Kaisa sits on the outer rim of a merry-go-round, and Chad sits midway between the rim and center. The
merry-go-round makes 1 revolution every 2 seconds. Chad’s angular velocity is ...
a. same as Kaisa’s
d. twice Kaisa’s
b. one-half of Kaisa’s
e. one-quarter of Kaisa’s
c. four times Kaisa’s
____ 10. An object at rest begins to rotate with a constant angular acceleration. If this object rotates through an angle
q in the time t, through what angle did it rotate in the time 1/2 t?
a.
b.
c.
1
θ
2
3
θ
4
1
θ
4
d.
4θ
e.
2θ
2
ame: ________________________
ID: A
____ 11. Which of these are the basic SI units for torque?
m2
s2
m
b.
d. kg 2
m
s
____ 12. Two spheres have the same mass. One sphere is made of aluminum, while the other sphere is made of gold.
Both are solid. Because gold is more dense, the radius of the gold sphere is smaller than the aluminum
sphere. Which has the larger moment of inertia?
a.
kg
m
s
c.
kg
a. aluminum sphere
c. both the same
b. gold sphere
d. not enough information
____ 13. When you pay the electric company for so many kilowatt-hours, what exactly are you paying for?
a. voltage
d. none of these
b. energy
e. power
c. current
____ 14. An open cart rolls along a frictionless track while it is raining. As it rolls, what happens to the speed of the
cart?
a. nothing
c. speeds up
b. not enough information given
d. slows down
____ 15. A small car and large truck collide head-on and stick together. Which has the larger change in momentum?
a. the less massive car
c. neither, they have the same change in
momentum
b. the more massive truck
d. not enough information given
3
ame: ________________________
ID: A
Problem
16. (10 pts) Derive the moment of inertia for a thin rod of mass M and length L that rotates about it’s center as
shown in this figure: (show all steps)
-
4
ame: ________________________
ID: A
17. (10 pts) A force F = 23i - 15j + 20k N is applied to a body as it moves in a straight line from
r1= 16i +3j-10k to r 2 = 5i + 10j+ 14k m. How much work is done by the force?
-
5
ame: ________________________
ID: A
18. (15 pts) A roller coaster cart with mass 1000 kg slides along the frictionless track shown in
this figure, starting at rest from point A. Find (a) its speed at D and (b) its speed at E.
(c) Now, consider that you wish to stop the cart at point E. A spring, with a spring constant
of 10000 N/m, is placed at point E to absorb the energy of the oncoming cart. By how
much will the spring compress when the cart comes to rest?
6
ame: ________________________
ID: A
19. (20 pts) A bug, fitted with a metal collar, slides back and forth in a bowl 11 cm deep,
starting from rest at the top, as shown in this figure. The bug has a mass of 10 g.The bowl
is frictionless, but, at the bottom, a magnetic force acts on the bug over a 1.5 cm patch.
This force is dependent on the position of the bug as defined by this function:
F = ax 3 / 2
where a=1.25 N/m 3/2. Assume the force acts symmetrically (that is, the same force is
experienced regardless of the bug’s direction).
a) What is the bug’s total energy at the top of the bowl?
b) How much energy does the bug lose when it crosses through the magnetic field?
c) What is the bug’s speed at the bottom on its first pass, just after it goes across the
magnetic patch?
d)How many times does the bug cross the 1.5 cm patch?
-
7
ame: ________________________
ID: A
20. (15 pts) At the MIT Magnet Laboratory, energy is stored in huge solid flywheels of mass 3.3
X 104 kg and radius 1.4 m. The flywheels ride on shafts 21 cm in diameter. A frictional
force of 28 kN acts tangentially on the shaft.
a) How long will it take the flywheel to coast to a stop from its normal rotation rate of 420
rpm?
b) What angular displacement (in radians) does the flywheel turn through in this time?
8
ID: A
Exam 2--PHYS 101-Fall 2009
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
ANS:
D
B
D
A
C
D
A
B
A
C
C
A
B
D
C
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
PTS:
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
DIF: 1
PROBLEM
16. ANS:
PTS: 1
17. ANS:
PTS: 1
18. ANS:
PTS: 1
19. ANS:
PTS: 1
20. ANS:
PTS: 1
1
TOP: 6.2 Conservation of Momentum