Clicker questions
A wave travelling in the +x direction is described by the equation y=0.1sin(10x− 100t), where x and y are in meters and t is in seconds. Calculate (i) the wavelength, (ii) the period, (iii) the speed, and (iv) the amplitude of the wave
(i) 0.63 m, (ii) 0.063 s, (iii) 10 m/s, (iv) 0.1 m
Organ pipe B is open at both ends and is half as long as organ pipe A, which is open at one end, as shown. What is (i) the ratio of their fundamental wavelengths λA : λB and (ii) the ratio of their fundamental frequencies fA : fB ?
(i) 4:1 (ii) 1:4
Which of the following wave functions describe a wave that moves in the -x-direction? 1. y(x,t) = A sin (-kx - ωt) 2. y(x,t) = A sin (kx + ωt) 3. y(x,t) = A cos (kx + ωt)
1,2,and3
If the intensity of a 40 dB sound is increased to 80 dB, the intensity in W/m2 increases by a factor of
10^4.
Assume that a naked human body has a surface area of 1.5 m2 and a surface temperature of 32oC. If the surroundings are at a temperature of 16oC, calculate the net rate of heat loss by the body due to radiation. Assume an emissivity of 1.
143 W
5 moles of a monatomic gas has its pressure increased from 105 Pa to 2*105 Pa. This process occurs at a constant volume of 0.1 m3. internal energy of the gas.
15000 J
A pure sound notes from a sources make the molecules of air at a location vibrate simple harmonically in accordance with the equation y1 = 0.008 sin (302 π t). What is the frequency of the sound wave?
151 Hz
A sample of water at 0 oC is slowly converted into ice at 0 oC? The entropy of the sample changes by ΔS = -0.586 kcal/K. the mass of the sample? The latent heat of fusion is 80 kcal/kg.
2kg
Two dice are thrown. Let the macrostate be the sum of the two numbers on the top faces. What is the multiplicity of the macrostate "4"?
3
You are watching a mass oscillate on a spring. The initial amplitude is 40 cm. The amplitude halves after 10 s. How long does it take for the amplitude of the oscillation to decrease to 5 cm?
30s
A string of length 100 cm is held fixed at both ends and vibrates in a standing wave pattern. The first harmonic is shown. The wavelengths of the standing waves making up the pattern cannot be
400 cm
A string of length 100 cm is held fixed at both ends and vibrates in a standing wave pattern. The first harmonic is shown. The wavelengths of the standing waves making up the pattern cannot be
400 cm.
Ice initially at -20 oC is to be turned into steam at 130 oC. To figure out how much heat is required, how many separate terms will there be?
5
A steel bridge is built in several segments, each 20 m long. The gap between segments is 2 cm at 18 oC. What is the maximum temperature that the bridge can manage before buckling?
95 oC
The positions of a dot is shown at successive 1-second time intervals. Which statements are true? (A) The dot is moving with constant speed. (B) The dot is moving with constant velocity. (C) The dot is accelerating.
A and C
Which one of the following situations is not possible?
A body travels with a constant velocity and a time-varying acceleration.
If ∆ = 1 m and the speed of sound is 340 m/s, which statement is correct?
All of the above statements are correct.
Which sounds travel the fastest through air?
All sound travels at the same speed through air.
The diagram shows the trajectory of a golf ball. Which set of arrows shows the direction of the acceleration at points P and Q respectively?
B
Water with air bubbles flows through a pipe that becomes narrower. Compared to the wider region, the bubbles in the narrow region are
Bigger
You need to loosen a very tight bolt. You have one wrench and you exert maximum force. Which configuration shown below gives you maximum chance of success?
C
A disk is spinning with angular velocity ω as shown. It begins to speed up. While it is speeding up, what are the (i) directions of its angular velocity ω (ii) and its angular acceleration α?
C,C
Two flutists are tuning up. If the conductor hears the beat frequency increasing, are the two flute frequencies getting closer together or father apart?
Farther apart
Orange growers in Florida spray their trees with water when they expect a freeze. Why does this work?
If a mixed phase of water and ice is present, the temperature does not drop below 0 oC.
A simple pendulum of length L oscillates back and forth 10 times per second. By what factor do you have to change its length to make it oscillate back and forth only 5 times per second?
Increase the length by a factor of 4.
Consider the change a gas undergoes as it transitions from point c to point a in the PV diagram. What type of process is this?
Isobaric
A gas, confined to an insulated cylinder, is compressed adiabatically (and reversibly) to half its original volume. Does the entropy of the gas increase, decrease, or remain unchanged during this process?
It remains unchanged.
Is it possible to cool down a well insulated room on a hot summer day by leaving the refrigerator door open, and using the refrigerator as an air conditioner?
No
When a car is at rest, its horn emits a sound wave of wavelength 0.55 m. A person standing in the middle of the street hears the horn with a frequency of 560 Hz. If the speed of sound is 330 m/s, should the person jump out of the way?
No
Your friend asks you to stand perfectly still holding up a weight bar with weights while he takes a picture. Are you doing work during this time?
No
A bowling ball rolls down an alley and hits a bowling pin. Which statement below is true about the magnitudes of the forces exerted during the impact?
The magnitudes of the forces that they exert on each are equal.
A chair has a wooden seat but metal legs. The chair legs feel colder to the touch than does the seat. Why?
The metal has a higher thermal conductivity than the wood.
Why does heat, of itself, not flow from a cold to a hot object, if it is allowed by Newton's laws?
This would require a large departure from equilibrium, which is extremely unlikely.
Assume the car is accelerating towards the right and its speed is increasing. A cup of coffee left on the roof is accelerating with the car at the same rate. What is the direction of the frictional force on the cup?
Towards the right
It is possible for heat to flow across vacuum.
True
The velocity versus time graph to the right represents the motion of an object moving in one dimension along the x-axis. The velocity of the object is always positive.
True
You are trying to bring a pot of water to a boil, to boil some eggs. To use the least amount of gas (energy), do the following.
Turn the flame on high.
The water is now boiling. To boil the eggs using the least amount of gas do the following.
Turn the flame on low, so that the water is barely boiling.
We flip a fair coin 10 times. Define a macrostate to be the number of heads. Define each microstate as a a particular sequence of heads and tails. Some microstates for coin flips are listed below. "H" stands for heads and "T" stands for tails. Rank the microstates from most likely to least likely to occur
VI) = III) = II) = I)
Your dryer is broken, so you have to hang your wet clothes from the washing machine outside to dry. Under which conditions would your clothes dry fastest?
When it is 75°F with 50% relative humidity.
It is possible for heat to enter a system while the temperature of the system to does not change?
Yes
Suppose you work in the E.R. and a choking patient comes in with their trachea half obstructed. (The diameter is half of what it was before the obstruction.) You manage to correct the problem and send them on their way safely, explaining that such obstructions are particularly dangerous because
a half - blocked airway passes only 1/16 the regular amount of air.
As a sound source approaches and then moves past a stationary observer, the observer will hear
a sudden drop in pitch.
A rock is thrown from the roof of a tall building. While it is falling towards the ground, the force of gravity acting on it is
equal to its weight.
The four strings of a musical instrument are all made of the same material and are under the same tension, but have different thicknesses. Waves travel
fastest on the thinnest string.
The _______ the temperature difference between hot and cold, the larger the fraction of heat you can divert and transform into __________.
larger; work
An ideal gas in a closed container with a piston lid is taken from thermodynamic state, 1, to a new thermodynamic state, 2, by an isothermal path as shown below in the P-V plane.
positive
People fighting forest fires carry emergency tents that have shiny aluminum outer surfaces. If there is trouble, a fire fighter can lie under the tent to block the heat from burning trees overhead. The tent helps because?
radiation carries heat downward toward the fire fighter and the aluminum tent reflects most of that radiation.
A simple pendulum consists of a point mass m suspended by a massless, unstretchable string of length L. If the mass is doubled while the length of the string remains the same, the period of the pendulum
remains unchanged.
Two objects with different masses collide and stick to each other. Compared to before the collision, the system of two objects after the collision has
the same total momentum but less total kinetic energy.
A pitcher contains 0.50 kg of liquid water and 0.50 kg of ice at 0°C. You let heat flow into the pitcher until there is 0.75 kg of liquid water and 0.25 kg of ice. During this process?
the temperature of the ice-water mixture remains the same.
A child playing with very smooth blocks on a very smooth, (frictionless), horizontal table pushes one of the blocks across the table. After the push, when the child's hand is no longer touching the block, the block continues to move with constant velocity because
there is no net force acting on the block.
Near the surface of the earth, the fluid at the bottom of a container is
under more pressure than the fluid on the top.
If you double the wavelength λ of a wave on a string under fixed tension, what happens to the wave speed v and the wave frequency f?
v is unchanged and f is halved.
Consider two specimens of ideal gas at the same temperature. The molecules in specimen #1 have greater molar mass than the molecules in specimen #2. How do the root-mean-square or RMS speeds, vrms = √<v2>, of molecules and the average translational kinetic energy per molecule, <KE> = 1⁄2m<v2>, compare in the two specimens?
vrms is greater in specimen #2; <KE> is the same in both specimens.
An ideal gas in a closed container with a piston lid is taken from thermodynamic state, 1, to a new thermodynamic state, 2, by an isothermal path as shown below in the P-V plane.
zero, because it is an isothermal process.
Position, velocity and acceleration of an oscillating mass on a spring are shown as a function of time. What is the period of the oscillations?
~2.5 s
Measure the frequency or period of a 0.1 kg mass oscillating on a spring. What is the spring constant of this spring?
~3 N/m
Position, velocity and acceleration of an oscillating mass on a spring are shown as a function of time. If the mass is 1 kg, what is the spring constant in N/m?
~6
