PHY EXAM 4
An object of mass m is attached to a horizontal spring, stretched to a displacement A from equilibrium and released, undergoing harmonic oscillations on a frictionless surface with period T0. The experiment is then repeated with a mass of 4m. Choose the new period of oscillation.
2T0
Stars A and B have the same temperature, but star A has twice the radius of star B. What is the ratio of star A's power output to star B's output due to electromagnetic radiation? The emissivity of both stars can be assumed to be 1.
4
Star A has twice the absolute temperature and twice the radius of star B. What is the ratio of star A's power output to star B's output due to electromagnetic radiation?
64
By visual inspection, order the PV diagrams shown in the figure from the most negative work done on the system to the most positive work done on the system.
a, c, b, d
True or False: A nonideal engine operating between the same temperature extremes as a Carnot engine and having the same input thermal energy will perform the same amount of work as the Carnot engine.
- False. Since the Carnot engine has the greatest efficiency possible, other engines operating between the two temperatures produce less useful work output for the same work input. - False. Carnot engines do not really exist. All real engines are less efficient.
Given that bone and muscle are denser than fat, what physical characteristics differentiate "sinkers" (those who tend to sink in water) from "floaters"
- Floaters tend to have more fat. - Sinkers tend to have heavier bones.
Is the frequency of vibration of a heavy vehicle greater or smaller than that of a lighter vehicle, assuming the two vehicles are supported by the same set of springs? Explain.
- The heavier vehicle has the lower frequency according to the expression for frequency f in terms of k and mass m. - The heavier vehicle has the lower frequency. Greater weight implies greater mass, less rapid acceleration by the spring, and slower vibration.
From the point of view of physics, does the answer depend on how fast the repetitions are performed? How do faster repetitions affect human metabolism?
- The number of repetitions stays the same. - The rate of metabolism increases.
What effect would doubling the initial amount of liquid water have on the amount of ice melted?
- Twice as much of the ice will melt. - The final temperature will be the same.
If the raft is placed in salt water, which has a density greater than fresh water, the value of h would:
- decrease because each cubic meter of salt water displaced weighs more than fresh water. - decrease because less volume of salt water must be displaced to have its weight equal that of the raft.
Why do water containers and gas cans often have a second, smaller cap opposite the spout through which the fluid is poured?
- to let air flow in as liquid is poured out - to keep the space above the liquid at the same pressure as outside while pouring
Why doesn't the melting of ocean-based ice raise as much concern and the melting of land-based ice?
1. Unlike land-based ice, ocean-based ice already displaces water, so when it melts ocean levels won't change much.
Star A has twice the absolute temperature of star B, but they both have the same radius. What is the ratio of star A's power output to star B's output due to electromagnetic radiation?
16
An object of mass m is attached to a horizontal spring, stretched to a displacement A from equilibrium and released, undergoing harmonic oscillations on a frictionless surface with period T0. The experiment is then repeated with a mass of 4m. What's the new period of oscillation?
2T0
A block on the end of a horizontal spring is pulled from equilibrium at x = 0 to x = A and released. Through what total distance does it travel in one full cycle of its motion?
4A
A block on the end of a spring is pulled to position x = A and released. Through what total distance does it travel in one full cycle of its motion?
4A
What are the different paths in the figure?
A: isovolumetric; B: adiabatic; C: isothermal; D: isobaric
Calculate the slopes for the A, C, and E portions of the figure. Rank the slopes from least to greatest.
C, A, E
Three engines operate between reservoirs separated in temperature by 300 K. The reservoir temperatures are as follows: Engine A: Th= 1 000 K, Tc = 700 K Engine B: Th = 800 K, Tc = 500 K Engine C: Th = 600 K, Tc = 300 K Rank the engines in order of their theoretically possible efficiency, from highest to lowest.
C, B, A
When an ideal gas expands at constant pressure, is the change in the internal energy positive or negative?
It is positive.
Objects A, B, and C are at different temperatures, A lowest and C highest. The three objects are put in thermal contact with each other simultaneously. Without doing a calculation, is it possible to determine whether object B will gain or lose thermal energy?
No. It depends partly on the initial temperatures, specific heats, and masses of A, B, and C.
Is the frequency of a wave affected by the wave's amplitude?
No. They are independent of each other.
Two spheres are made of the same metal and have the same radius, but one is hollow and the other is solid. The spheres are taken through the same temperature increase. Which sphere expands more?
They expand by the same amount.
You observe two helium balloons floating next to each other at the ends of strings secured to a table. The facing surfaces of the balloons are separated by 1-2 cm. You blow through the opening between the balloons. What happens to the balloons?
They move toward each other.
True or False: If a guitar string has length L, gently placing a thin object at the position ½nL will always result in the sounding a higher harmonic, where n is a positive integer.
True. But only some of the harmonics are produced by following that procedure.
Two rods of the same length and diameter are made from different materials. The rods are to connect two regions of different temperature so that energy will transfer through the rods by heat. They can be connected in series, as in figure a, or in parallel, as in figure b. In which case is the rate of energy transfer by heat larger?
When the rods are in parallel.
Does the Doppler shift change due to temperature variations? If so, why? For typical daily variations in temperature in a moderate climate, would any change in the Doppler shift be best characterized as nonexistent, small, or large?
Yes. A change in temperature changes the speed of sound and the Doppler shift, causing changes of a few percent.
Compared to an identical ice cube exposed to air at room temperature, an ice cube wrapped in a wool blanket remain frozen for
a longer time.
When an object moving in simple harmonic motion is at its maximum displacement from equilibrium, which of the following is at a maximum?
acceleration
Suppose you have one cubic meter of gold, two cubic meters of silver, and six cubic meters of aluminum. Rank them by mass, from smallest to largest.
aluminum, gold, silver
A simple pendulum is suspended from the ceiling of a stationary elevator, and the period is measured. If the accelerates upward, the period
decreases
An object of mass m is attached to a horizontal spring, stretched to a displacement A from equilibrium and released, undergoing harmonic oscillations on a frictionless surface. The experiment is then repeated with a mass of 4m. Compared to the original total mechanical energy, the subsequent total mechanical energy of the object with mass 4m is
equal
The density of lead is greater than that of iron, and both are denser than water. Compared to a solid iron object of the same dimensions, the buoyant force acting on a solid lead object is
equal
Several common barometers are built using a variety of fluids. For which fluid will the column of fluid in the barometer be the highest?
ethyl alcohol (least dense)
True or False: In an isothermal process no thermal energy transfer takes place.
false
Two objects with different sizes, masses, and temperatures are placed in thermal contact. Choose the best answer. Energy travels
from the object at higher temperature to the object at lower temperature.
If you are asked to make a very sensitive glass thermometer, which of the following working fluids would you choose?
gasoline (highest coefficient of expansion)
The period of a simple pendulum is measured to be T on Earth. If the same pendulum were set in motion on the Moon, its period would be which of the following?
greater than T
The period of a simple pendulum is measured to be T on the Earth. If the same pendulum were set in motion on the Moon, would its period be
greater than T
Blood pressure is normally measured with the cuff of the sphygmomanometer around the arm. Suppose that the blood pressure is measured with the cuff around the calf of the leg of a standing person. The reading of the blood pressure will be
greater than it is for the arm
Suppose you have 1 kg each of iron, glass, and water, and all three samples are at 10°C. Rank them from least to greatest amount of energy transferred by heat if enough energy is transferred so that each increases in temperature by 20°C.
iron, glass, water
Suppose you are throwing two dice in a friendly game of craps. For any given throw, the two numbers that are face up can have a sum of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. Which outcome is most probable? Which outcome is least probable?
most probable: 7; least probable: 2 and 12
If no energy were added to the gas during the expansion, could the pressure remain constant?
no
Atmospheric pressure varies from day to day. The level of a floating ship on a high-pressure day is
no different than on a low-pressure day.
If the amplitude of a system moving in simple harmonic motion is doubled, which of the following quantities doesn't change?
period
For a simple harmonic oscillator, which of the following pairs of vector quantities can't both point in the same direction? (The position vector is the displacement from equilibrium.)
position and acceleration
A simple pendulum is suspended from the ceiling of a stationary elevator, and the period is measured. If the elevator moves with constant velocity, the period
remains the same.
A pendulum clock depends on the period of a pendulum to keep correct time. Suppose a pendulum clock is keeping correct time and then Dennis the Menace slides the bob of the pendulum downward on the oscillating rod. Does the clock run slow, fast, or correctly?
slow
A pendulum clock depends on the period of a pendulum to keep correct time. Suppose a pendulum clock is keeping correct time and then Dennis the Menace slides the bob of the pendulum downward on the oscillating rod. The clock then runs
slow.
The pressure at the bottom of a glass filled with water r = 1 000 kg/m3) is P. The water is poured out and the glass is filled with ethyl alcohol (r = 806 kg/m3). The pressure at the bottom of the glass is now
smaller than P.
Rank by the amount of fractional increase in length under increasing tensile stress, from smallest to largest: rubber, tungsten, steel, aluminum
tungsten < steel < aluminum < rubber
Suppose you have 1 kg each of iron, glass, and water, and all three samples are at 10°C. Rank the samples from lowest to highest temperature after 100 J of energy is added to each by heat.
water, glass, iron
A wave in one medium encounters a new medium and enters it. Which of the following wave properties will be affected in this process?
wavelength, speed
Which of the following is true for the entropy change of a system that undergoes a reversible, adiabatic process?
Δs = 0