Download General Physics – ph 211

General Physics – ph 201
Midterm Exam II (Ch 4 – 6)
November 14, 2005
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Name:____________
Type A
Exam is closed book and closed notes. Use only your note card.
Write all work and answers in the papers provided.
Show all your work and explain your reasoning (No credit will be
given for an answer that does not include the necessary solution or
explanation, except for true/false or multiple choice questions)
Partial credit may be awarded for a correct method of solution, even if the
answer is wrong.
Part I – True or False (2.5 points each): For questions 1 – 10, state whether each
statement is true or false.
0. My test type is ________.
1. The acceleration of an object does not have to be in the same direction as the net
force applied to it.
2. The force of static friction always equals sFN.
3. An object cannot move in a circle unless there is net force acting on it.
4. When a ball is thrown upward, it reaches its maximum height when the force
pushing it up is equal to its weight.
5. A box sits on a table. The normal force of the table on the box equals in magnitude the
weight of the box because of Newton's Second Law.
6. The drag force on an object falling through air is a conservative force.
7. In the presence of frictional forces, the total mechanical energy always decreases.
8. Two blocks of different masses are projected up a rough inclined plane with the same
initial speed. Both blocks reach the same height.
Part II – Multiple Choice (2.5 points each): Choose the one correct answer for each of
the following questions that best answers or completes the question.
11. A horizontal force measured with a spring scale is applied to a box sitting on a table. Until
the force is increased to a particular value the box does not move. Just as the box starts
moving the reading on the spring scale
A) remains the same
C) increases.
B) Decreases
D) more information is needed.
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12. A heavy box of mass 50 kg sits at rest on a floor. The coefficients of static and kinetic
friction between the box and the floor are 0.4 and 0.35 respectively. A force of 150 N is
applied horizontally to the box. The box will
A) move at constant velocity
B) accelerate
C) remain at rest forever
D) remain at rest for 2 s and then accelerate
13.
A bucket of mass 2 kg is whirled in a vertical circle of radius 1 m. At the lowest point of its
motion the tension in the rope supporting the bucket is 25 N. The speed of the bucket is
A) 1.6 m/s
A) 4.7 m/s
B) 2.7 m/s
D) 5.6 m/s
14.
A puck sits on a rotating turntable rotating at a constant rate. If the puck is placed at a
distance of 10 cm from the center of the turntable, the puck flies off if the rotation rate
exceeds 0.5 rev/s. The coefficient of static friction in the above problem is
A) 0.1
C) 0.3
B) 0.2
D) 0.4
15.
Four equal masses are located at the corners of a square. The direction of the gravitational
force at the midpoint of the lower side of the square is
A) up.
C) left.
B) down.
D) right.
16. Two satellites are in circular orbits about the Earth, with satellite 2 in an orbit of larger
radius than satellite1. Which satellite has the larger speed?
A) satellite 1
B) satellite 2
C) need to know the masses of the satellites
18.
A box is given an initial velocity of 5 m/s. It slides across a rough surface coming to rest in
2 m. The coefficient of kinetic friction is
A) 0.2
C) 0.6
B) 0.4
D) 0.7
24. A block whose weight is 20 N rests on a horizontal surface. The coefficient of static
friction between the block and supporting surface is 1.0. A string is attached to the
block. The tension in the string is 20 N, and the string makes an angle of 30o with
the horizontal.
T = 20 N
300
A)
B)
C)
D)
The block will remain at rest, and fs = 17.3N
20 N
s=1.0
The block will move horizontally
The block will be lifted off the surface by the string.
The block will remain at rest; the force of static friction is less than 17.3 N.
26. A ball is tied to the end of a string and swung in a vertical circle on earth. The
speed of the ball is kept constant. The tension in the string is
A) larger at the top.
C) the same at top and bottom.
B) larger at the bottom.
Ph 201 midterm 2, f2005
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27. What is (are) the SI units of force divided by mass.
A) kg
B) m/s
C) kg m/s2
28.
29.
D) m/s2
E) J
A uniform solid sphere has mass M and radius R. If these are increased to 2M and
3R, what happens to the sphere's moment of inertia about a central axis?
a. Increases by a factor of 6.
b. Increases by a factor of 12.
c. Increases by a factor of 18.
d. Increases by a factor of 54.
If a constant net torque is applied to an object, that object will
a. rotate with constant angular velocity.
b. rotate with constant angular acceleration.
c. having an increasing moment of inertia.
d. having a decreasing moment of inertia.
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Part III – Problems (10 points each): Show your work clearly and completely for each
of the following problems.
30. A 4.48 kg block is pushed along the ceiling with a constant applied force of 86.3 N
that acts at an angle of 63.0o with the horizontal as shown in the figure. The block
accelerates to the right at 6.00 m/s2.
86.3N
A)
B)
Draw the freebody diagram showing all forces.
63o
Find the coefficient of kinetic friction between the block and the ceiling.
31. Suppose the coefficient of kinetic friction between m1 and the plane in Figure shown
below is  k  0.15, and that m1  m2  2.7 kg. As m 2 moves down,
A) Draw a free body diagram for each mass, showing all forces; include
direction of acceleration for each mass too.
B) Determine the magnitude of the acceleration of m1 and m2 , given   25 º.
C) What smallest value of  k will keep this system from accelerating?
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32. A passenger on the Ferris wheel normally weighs 403 N. The Ferris wheel has a 25 m
radius and is equipped with a powerful motor. The operator revs it up so that the
customers at the top of the wheel feel zero g's (they momentarily lift slightly off their
seats).
A) At what angular velocity will this occur?
B) If the rotating angular velocity remains the same as in Part A. What weight
does the customer feel at the bottom of the wheel? Answer in units of N.
33. An earth satellite remains in orbit at a distance of r = 7130 km from the center of the
earth. What speed would it have to maintain?
G = 6.67 × 10-11N. m2/kg2 and Mearth = 5.98 × 1024 kg.
How many radians does a 0.300-m radius automobile tire rotate after starting from
rest and accelerating at a constant angular acceleration of 2.00 rad/s‚ over a 5.00-s
interval?
34.
A wheel of moment of inertia of 5.00 kg m2‚ starts from rest and accelerates under
a constant torque of 3.00 N m for 8.00 s. What is the wheel's rotational speed at the
end of 8.00 s?
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