Download Version B - UCSB High Energy Physics Home Page

Physics 6b Winter 2015 Midterm Test Form B • Fill out name and perm number on the scantron. • Do not forget to bubble in the “Test Form” (A, B, C, or, D). • At the end, only turn in the scantron. Keep questions/cheat sheets, etc. • You may want to keep a record of your answers to double-­‐check the scantron results. (Solutions will be provided). Do not turn this page until you have been instructed to do so 1
1) The figure shows two unequal point charges, q and Q, of opposite sign. Charge Q has greater magnitude
than charge q. In which of the regions X, Y, Z will there be a point at which the net electric field due to these
two charges is zero?
A) only regions X and Z
B) only region X
C) only region Y
D) only region Z
E) all three regions
2) A positive point charge Q is fixed on a very large horizontal frictionless tabletop. A second positive point
charge q is released from rest near the stationary charge and is free to move. Which statement best describes
the motion of q after it is released?
A) As it moves farther and farther from Q, its acceleration will keep increasing.
B) As it moves farther and farther from Q, its speed will decrease.
C) As it moves farther and farther from Q, its speed will keep increasing.
D) Its speed will be greatest just after it is released.
E) Its acceleration is zero just after it is released.
3) A standing wave is oscillating at 690 Hz on a string, as shown in the figure. What is the speed of traveling
waves on this string?
A) 410 m/s
B) 140 m/s
C) 280 m/s
D) 210 m/s
4) The weight of a car of mass 1.20 × 10 3 kg is supported equally by the four tires, which are inflated to the
same gauge pressure. What gauge pressure in the tires is required so the area of contact of each tire with the
road is 1.00 × 10 2 cm2? (1 atm = 1.01 × 10 5 Pa.)
A) 2.94 × 10 4 Pa
B) 2.94 × 10 3 Pa
C) 11.6 × 10 5 Pa
D) 2.94 × 10 5 Pa
E) 11.6 × 10 4 Pa
5) Water flows through a pipe having a varying width. More water flows per second through the wide section
than through the narrow section because there is more room for it to flow.
A) True
B) False
Physics 6B - Winter 2015
2
6) Two identical small charged spheres are a certain distance apart, and each one initially experiences an
electrostatic force of magnitude F due to the other. With time, charge gradually leaks off of both spheres.
When each of the spheres has lost half its initial charge, the magnitude of the electrostatic force will be
A) 1/16 F.
B) 1/8 F.
C) 1/2 F.
D) 1/4 F.
7) A rock is under water in a shallow lake. As the rock sinks deeper and deeper into water, the buoyant force on
it
A) remains constant.
B) increases.
C) decreases.
8) An object is attached to a vertical ideal massless spring and bobs up and down between the two extreme
points A and B. When the kinetic energy of the object is a minimum, the object is located
A) midway between A and B.
B) 1/4 of the distance from A to B.
C) at either A or B.
D) 1/ 2 times the distance from A to B.
E) 1/3 of the distance from A to B.
9) A certain frictionless simple pendulum having a length L and mass M swings with period T. If both L and M
are doubled, what is the new period?
A) T
B) 4T
C) 2T
D) 2T
E) T/4
10) In the figure Q = 5.8 nC and all other quantities are accurate to 2 significant figures. What is the magnitude of
the force on the charge Q? (k = 1/4!" = 8.99 × 10 9 N ∙ m 2/C2)
0
A) 1.8 × 10 -3 N
B) 1.2 × 10 -3 N
C) 1.0 × 10 -3 N
D) 9.0 × 10 -4 N
11) The density of aluminum is 2700 kg/m3. If transverse waves propagate at 34 m/s in a 4.6-mm diameter
aluminum wire, what is the tension on the wire?
A) 31 N
B) 42 N
C) 62 N
D) 52 N
12) Consider a pipe of length L that is open at both ends. What are the wavelengths of the three lowest-pitch
tones produced by this pipe?
A) 4L, 4L/3, 4L/5
B) 2L, L, L/2
C) 2L, L, 2L/3
D) 2L, L, L/2
E) 4L, 2L, L
Physics 6B - Winter 2015
3
13) A simple harmonic oscillator has an amplitude of 3.50 cm and a maximum speed of 26.0 cm/s. What is its
speed when the displacement is 1.75 cm?
A) 14.2 cm/s
B) 15.0 cm/s
C) 22.5 cm/s
D) 12.0 cm/s
E) 17.0 cm/s
14) A point charge Q is located a short distance from a point charge 3Q, and no other charges are present. If the
electrical force on Q is F, what is the electrical force on 3Q?
A) F/3
B) F
C) F/ 3
D) 3F
E) 3F
15) In simple harmonic motion, the speed is greatest at that point in the cycle when
A) the potential energy is a maximum.
B) the magnitude of the acceleration is a maximum.
C) the kinetic energy is a minimum.
D) the magnitude of the acceleration is a minimum.
E) the displacement is a maximum.
16) A cup of water containing an ice cube at 0°C is filled to the brim. The tip of the ice cube sticks out of the
surface. As the ice melts, you observe that
A) the cup overflows.
B) the cup might overflow but it depends on the actual mass of the ice cube.
C) the water level actually goes down.
D) the water level remains the same.
E) There is not enough information to answer this question.
17) A 1.0-C point charge is 15 m from a second point charge, and the electric force on one of them due to the
other is 1.0 N. What is the magnitude of the second charge? (k = 1/4!" = 8.99 × 10 9 N ∙ m 2/C2)
0
A) 25 C
B) 10 nC
C) 25 nC
D) 0.025 C
E) 1.0 C
18) A certain coin has a diameter of 21.21 mm, a thickness of 1.95 mm, and weighs 0.04905 N. What is its
density?
A) 29.1 × 10 3 kg/m 3
B) 2.31 × 10 3 kg/m 3
C) 9.25 × 10 3 kg/m 3
D) 7.26 × 10 3 kg/m 3
E) 71.2 × 10 3 kg/m 3
19) Two people are talking at a distance of 3.0 m from where you are and you measure the sound intensity as 1.1
× 10 -7 W/m 2. Another student is 4.0 m away from the talkers. What sound intensity does the other student
measure? Assume that the sound spreads out uniformly and undergoes no significant reflections or
absorption.
A) 8.3 × 10 -8 W/m 2
B) 7.8 × 10 -7 W/m 2
C) 1.5 × 10 -7 W/m 2
D) 6.2 × 10 -8 W/m 2
E) 2.5 × 10 -8 W/m 2
Physics 6B - Winter 2015
4
20) An object of mass 8.0 kg is attached to an ideal massless spring and allowed to hang in the Earth's
gravitational field. The spring stretches 3.6 cm before it reaches its equilibrium position. If this system is
allowed to oscillate, what will be its frequency?
A) 2.1 Hz
B) 0.67 Hz
C) 0.0045 Hz
D) 2.6 Hz
21) A frictionless pendulum clock on the surface of the earth has a period of 1.00 s. On a distant planet, the
length of the pendulum must be shortened slightly to have a period of 1.00 s. What is true about the
acceleration due to gravity on the distant planet?
A) We cannot tell because we do not know the mass of the pendulum.
B) The gravitational acceleration on the planet is equal to g.
C) The gravitational acceleration on the planet is slightly less than g.
D) The gravitational acceleration on the planet is slightly greater than g.
22) X and Y are two uncharged metal spheres on insulating stands, and are in contact with each other. A
positively charged rod R is brought close to X as shown in Figure (a).
Sphere Y is now moved away from X, as in Figure (b).
What are the final charge states of X and Y?
A) X is negative and Y is positive.
B) X is neutral and Y is positive.
C) Both X and Y are negative.
D) X is positive and Y is neutral.
E) Both X and Y are neutral.
23) A guitar string is fixed at both ends. If you tighten it to increase its tension
A) the frequencies of its vibrational modes will increase but its wavelengths will not be affected.
B) the wavelength increases but the frequency is not affected.
C) both the frequency and the wavelength increase.
24) A mass M is attached to an ideal massless spring. When this system is set in motion with amplitude A, it has
a period T. What is the period if the amplitude of the motion is increased to 2A?
A) 2T
B) T/2
C) 4T
D) 2T
E) T
Physics 6B - Winter 2015
5
25) Four traveling waves are described by the following equations, where all quantities are measured in SI units
and y represents the displacement.
I: y = 0.12 cos(3x - 21t)
II: y = 0.15 sin(6x + 42t)
III: y = 0.13 cos(6x + 21t)
IV: y = -0.27 sin(3x - 42t)
Which of these waves have the same period?
A) I and IV, and also II and III
B) I and III, and also II and IV
C) I and II, and also III and IV
D) All of them have the same period.
E) They all have different periods.
Physics 6B - Winter 2015
Answer Key
Testname: MIDTERM-B
1) B
2) C
3) C
4) D
5) B
6) D
7) A
8) C
9) D
10) A
11) D
12) C
13) C
14) B
15) D
16) D
17) C
18) D
19) D
20) D
21) C
22) A
23) A
24) E
25) B
Physics 6B - Winter 2015