代写Phys 123 Midterm exam 1代写数据结构语言程序
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Midterm exam 1
I. Lecture multiple choice (45 points - 9 questions)
1) (5 pts) The graph shows the displacement of an object undergoing simple harmonic motion versus time. What is the angular frequency of the object?
A. 4.2 s-1
B. 2.0 s-1
C. 1.5 s-1
D. 0.67 s-1
E. 0.34 s-1
2) (5 pts) Two identical blocks oscillate on different horizontal springs (A and B) . Which spring has the larger spring constant?
A. Spring A
B. Spring B
C. Both springs had the same spring constant
D. Need more information.
3) (5 pts) A mass on the end of a horizontal spring is pulled 3.0 cm from the equilibrium position and released. In two full cycles of its motion, through what total distance does it travel?
A. 6.0 cm
B. 15 cm
C. 20 cm
D. 24 cm
E. 30 cm
4) (5 pts) A 23 kg object is undergoing lightly damped harmonic oscillations. If the total energy drops to 1/6th its original value in 2.1 s, what is the value of the time constant for damping, τ?
A. 1.2 s
B. 0.17 s
C. 3.1 s
D. 0.58 s
E. 2.1 s
5) (5 pts) One end of a string is attached to a vibrator and the other end goes over a pulley and has a weight hanging from it. The frequency of the vibrator is adjusted until only one node is observed between the pulley and the vibrator, as shown below.
Now the frequency of the vibrator is increased by a factor of 1.5. Is a standing wave observed, and if so, how many nodes are observed between the pulley and the vibrator?
A. No standing wave is observed.
B. A standing wave is observed with 1 node between pulley and the vibrator.
C. A standing wave is observed with 1.5 nodes between pulley and the vibrator.
D. A standing wave is observed with 2 nodes between pulley and the vibrator.
E. A standing wave is observed with 4 nodes between pulley and the vibrator.
6) (5 pts) A sound source emits a frequency fs. Two students measure the observed frequency of the sound source under two different conditions. Student A moves with a speed half the speed of sound toward the sound source while sound source is stationary. Student B is stationary while the sound source moves towards them at half the speed of sound. Which of the following statements is correct?
A. The frequency perceived by student A is greater than the frequency perceived by student B.
B. The frequency perceived by student A is less than the frequency perceived by student B.
C. The frequency perceived by student A is equal to the frequency perceived by student B.
D. Need more information.
7) (5 pts) The diagram at right shows the wavefronts from two small sources at one instant in time. The solid lines represent crests, and the dashed lines represent troughs. Rank the displacement from equilibrium of these points one-half period later. Note that maximum displacements below equilibrium would be the smallest.
A. Dp < DH < DQ
B. DQ < DH < Dp
C. DH < Dp = DQ
D. Dp = DQ < DH
E. DH < DQ < Dp
8) (5 pts) A sound engineer is standing in front of two speakers as shown. The speakers are emitting a frequency of 226.4 Hz, and the engineer hears a minimum sound (assume complete destructive interference). What is the minimum value of x in the diagram (x is less than 4.0 m)?
A. 3.60 m
B. 3.00 m
C. 2.50 m
D. 2.00 m
E. 1.52 m
9) (5 pts) A mask with two medium sized holes directly above each other is placed in front of a screen. A blue bulb is placed in front of the mask at the same height as the bottom hole, and a red blub is placed directly above the blue bulb, at the same height as the top hole, as shown at right. The holes are large enough that you can ignore diffraction. Which image below best represents what you would see on the screen?
III. Lab multiple choice (15 points)
10) (5 pts) In lab A1 you used Excel to make a simulation of a ball of mass m hanging from a vertical spring with spring constant k. Let y0, v0, and a0, respectively, represent the position, velocity, and acceleration of the ball at time t0 . You calculated the position and velocity a short time, dt, later using the equations: v1 = v0 + a0 *dtandy1 = y0 + v1 *dt, respectively. Which of the following statements are correct?
i. This method only works for simple harmonic motion.
ii. You could test different models for the force acting on the ball by modifying the equation for how a0 was calculated.
iii. The first equation assumes the acceleration is approximately constant during the time interval dt.
A. i. only
B. ii. only
C. iii. only
D. ii. and iii.
E. All of these statements are correct.
11) (5 pts) In lab A2 each member of your group measured the frequency at which they observed a standing wave. The function generator reports frequency to one decimal place, and the results obtained were 13.2 Hz, 14.0 Hz, 14.8 Hz, and 13.5 Hz. How would your group report the frequency of the standing wave?
A. 13.88 ± 0.05 Hz
B. 13.88 ± 0.70 Hz
C. 13.9 ± 0.05 Hz
D. 13.9 ± 0.7 Hz
E. 14 ± 1 Hz
12) (5 pts) In lab A3 your group varied the scaling factor for the mass of the balls on the right half relative to the left half , m, and measured the maximum amplitude of a pulse when the start of the pulse reached the last ball, A. You made the plot below from your measurements.
Which of the following best matches the conclusion you would reach from your data?
A. The trendline is not a good fit as it does not go through all the uncertainty bars.
B. The trendline is not a good fit as it goes through more than 2/3rds of the uncertainty bars.
C. The trendline is a good fit as it goes through more than 2/3rds of the uncertainty bars.
D. The trendline is not a good fit as it goes through less than 2/3rds of the uncertainty bars.
E. The trendline is a good fit as it goes through less than 2/3rds of the uncertainty bars.
III. Lecture free response (25 points)
Show your working and give full explanations to get full credit.
You attach one end of a slinky (spring) firmly to a tree and hold the other end. You then stretch the slinky so that it is 2.0 m long, as shown at right. At t = 0.0 s you start moving the end of the slinky you are holding vertically. The graph below shows the vertical displacement curve of point P on the slinky, which is halfway along the slinky.
A. (5 pts) What is the wave speed? Be sure to show how you determined your answer.
B. (5 pts) What is the speed of point P on the slinky at t = 0.75 s? Be sure to show how you determined your answer.
C. (5 pts) On the graph below, draw the wavefunction at t = 0.5 s? Be sure to label the tick marks on the horizontal axis such that we can determine the scale.
MORE QUESTIONS ON OTHER SIDE
You stand a distanced from a speaker that produces sound waves with a power of Ps. Assume the sound waves propagate uniformly in all directions and that your eardrums are circular with radius re . Answer the following questions in terms of variables given and constants.
D. (5 pts) What is the intensity of the sound received by one of your eardrums?
E. (5 pts) What is the power of the sound received by one of your eardrums?
IV. Tutorial free response (15 points)
Show your working and give full explanations to get full credit.
A. (5 pts) A pulse with a wave speed of 1.0 m/s is approaching either a fixed end or a free end of a spring. The shapes of the spring at t = 0 sand t = 0.4 s are shown at right. Is the shape of the spring at t = 0.4 s consistent with the end being fixed or free? Explain.
Two different springs are connected at a junction. A student generates a pulse at one end of the connected springs. The diagram below shows the shape of the springs a short time after the pulse reaches the junction, although the junction is not shown. You are not told which spring has a greater mass per unit length, or which end the student generated the pulse.
B. (5 pts) Clearly indicate on the diagram above where is the junction located? Explain.
C. (5 pts) Is the mass per unit length of the left spring greater than, less than, or equal to, the mass per unit length of the right spring? Explain.