Download Exam 2

PHYSICS 11 (Fall 2015)
Exam 2
Elementary Physics
October 19, 2015
Name:
Circle your Recitation:
A01
Myers
(8:30 a.m.)
A03
Yang
(11:40 a.m.)
A04
Pepe
(1:15 p.m.)
A08
Myers
(1:15 p.m.)
A05
Pepe
(2:50 p.m.)
A06
Sanders
(4:25 p.m.)
A07
Sanders
(6:00 p.m.)
A02
Yang
(7:35 p.m.)
INSTRUCTIONS:
For the multiple choice questions on pages 1–2,
you will be graded on the basis of your answer
only. You will get full credit for a correct answer,
zero credit for incorrect answers, zero credit for
choosing multiple answers even if one of them is
the correct response. There is only one correct
answer for each multiple choice question.
SCORE BOX
Page 1
(10)
For the problems on pages 3–5, you must show
your work in the form of a diagram, statement
and/or equation to get full credit, even if you write
down the correct answer. If your answer is incorrect, you will receive partial credit for steps taken
in the direction of the correct solution. So, show
all your work.
Page 2
(20)
Page 3
(15)
Page 4
(15)
No books or notes are permitted in this examination. Writing instruments and a calculator are the
only items that you will need.
Page 5
(15)
Total
(75)
** READ THE QUESTIONS CAREFULLY **
1. It is past midnight and Sue is sliding down a rope from her third floor window to meet her boyfriend. As she slides
down the rope faster and faster, she becomes frightened and grabs harder on the rope, increasing the tension in the
rope. As soon as the upward tension in the rope becomes equal to Sue’s weight,
(a)
(b)
(c)
(d)
Sue will continue down at a constant velocity.
Sue will slow down.
Sue will stop.
the rope must break.
ANSWER[
(5)
]
(score)
2. A ladybug hangs on for dear life to the outer edge of a turntable that spins with constant angular speed. What can be
said about the net force and net torque on the ladybug?
(a)
(b)
(c)
(d)
The net force is zero and the net torque is not zero.
The net force is not zero and the net torque is zero.
Both the net force and net torque are zero.
Neither the net force nor the net torque are zero.
ANSWER[
αβγδ
(5)
]
(score)
p. 1
page total:
PHYSICS 11 (Fall 2015)
Exam 2
Elementary Physics
October 19, 2015
Name:
3. As a car skids with its wheels locked trying to stop on a road covered with ice and snow, the force of friction between
the icy road and the tires will usually be
(a)
(b)
(c)
(d)
greater than the normal force of the road times the coefficient of static friction.
equal to the normal force of the road times the coefficient of static friction.
greater than the normal force of the road times the coefficient of kinetic friction.
less than the normal force of the road times the coefficient of static friction.
ANSWER[
(5)
]
(score)
4. A particular motor can provide a maximum torque of 110 N·m. Assuming that all of this torque is used to accelerate
a solid, uniform, cylindrical flywheel of mass 10.0 kg and radius 3.00 m, how long will it take for the flywheel to
accelerate from rest to 8.13 rad/s?
(a)
(b)
(c)
(d)
2.17 s
2.83 s
3.33 s
4.03 s
ANSWER[
(5)
]
(score)
5. A 60.0-kg man stands at one end of a 40.0-kg uniform 10.0-m long board. How far from the man is the center of mass
(or center of gravity) of the man-board system?
(a)
(b)
(c)
(d)
(e)
1.00 m
1.25 m
2.00 m
5.00 m
7.50 m
ANSWER[
(5)
]
(score)
6. A box, mass m, is sliding up a rough ramp that is inclined at an angle θ with respect to horizontal. Which of the
following expressions gives the magnitude of the acceleration of the box?
(a) g sin θ
(b) g cos θ + µk g sin θ
(c) g sin θ + µk g cos θ
(d) g sin θ − µk g cos θ
(e) µk g cos θ
ANSWER[
αβγδ
(5)
]
(score)
p. 2
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PHYSICS 11 (Fall 2015)
Exam 2
Elementary Physics
October 19, 2015
Name:
7. Two blocks, stacked on top of one another as shown in the figure, slide along a frictionless tabletop. The surface
between the blocks is rough, with static friction coefficient, µs = 0.60. A horizontal external force, F, acts on the 2.0
kg top block as shown.
(a) Draw separate free body diagrams for each box. Each diagram should clearly
indicate each force that acts on the box of interest, with a label that describes
the nature of each force. If any of the forces in your diagrams are equal and
opposite in the sense of Newton’s 3rd Law, indentify these forces.
(5)
(score)
(b) If the external force has a magnitude of 8.0 N, what is the magnitude of the frictional force that the 2.0 kg block
exerts on the 5.0 kg block?
(5)
(score)
(c) What is the maximum value F can have before the 2.0 kg block on top starts to slip?
(5)
(score)
αβγδ
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PHYSICS 11 (Fall 2015)
Exam 2
Elementary Physics
October 19, 2015
Name:
8. A "swing" ride at a carnival consists of chairs that are
swung in a circle by 15.0-m cables attached to a vertical
rotating pole, as the drawing shows. Suppose the total
mass of a chair and its occupant is 160 kg.
(a) Draw a free body diagram for the circling mass (chair + occupant treated as one system). For full credit, show
and label each force vector, indicate the direction of the net force, and show your coordinate axes.
(5)
(score)
(b) Determine the tension in the cable attached to the chair.
(5)
(score)
(c) Find the speed of the chair.
(5)
(score)
αβγδ
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PHYSICS 11 (Fall 2015)
Exam 2
Elementary Physics
October 19, 2015
Name:
9. Three small masses are attached together by rigid
lightweight rods as shown in the diagram to the right.
The 1.2 kg mass is located at the origin. The 9.0 kg mass
is located on the y axis at y = +1.0 m and the 2.5 kg mass
is located at x = + 2.0 m on the x axis. You may assume
each mass is small enough in size to be considered as a
geometric point, and that the rods are of negligible mass.
This rigid object is free to rotate about the z axis which
passes through the origin and is perpendicular to the plane
of this page.
There is a force, F , of magnitude 25.0 N that acts on the
9.0 kg mass. This force points entirely in the +x direction.
(a) Find the rotational inertia of this arrangement of masses about the rotation axis.
(5)
(score)
(b) Find the torque produced by F about the rotation axis at the time shown in the diagram
(5)
(score)
(c) Find the angular acceleration of this rigid object at the time shown in the diagram.
(5)
(score)
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