A concave mirror has a focal length of 63.6 cm.
(a) What is its radius of curvature?
__________ cm
(b) Locate the image when the object distance is 100 cm. (Indicate
the side of the mirror with the sign of your answer.)
____________ cm
Describe the properties of the image when the object distance is
100 cm. (Select all that apply.)
A) real
B) virtual
C) upright
D) inverted
(c) Locate the image when the object distance is 10.0 cm. (Indicate
the side of the mirror with the sign of your answer.)
________ cm
Describe the properties of the image when the object distance is
10.0 cm. (Select all that apply.)
A) real
B) virtual
C) upright
D) inverted
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Kinetic friction is a constant-value force, while static friction changed in response to other forces, up to some maximum. Why is this the case? What if static friction behaved more like kinetic friction, with same constant value?
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How far would you have to drill into the Earth, to reach a point where your weight is reduced by 7.5% ? Approximate the Earth as a uniform sphere.
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An astronaut wants to determine the mass of objects she finds in space. On Earth she chooses a spring and attaches a rock to it that weighs 20 N. After placing the rock on a horizontal table, and attaching the spring horizontally to a fixed point, she stretches the rock 2 cm from equilibrium, in the positive direction. She then releases it from rest. After 30 s has passed, she finds that the rock has gone through 10 cycles and is at a new positive maximum value, which is 1 cm from equilibrium. (a) What is the period of the oscillation? (b) What is the spring constant of the spring? (c) What is the time constant of the decay? (d) Find a function that describes the motion, including damping, of the spring and mass system that is only a function of time. Assume time starts when the mass is released. (e) Roughly sketch (1) the position vs time and (2) velocity vs time of this setup. (f) Later, during the return from a mission on Mars (no gravity), she wants to know the mass of an unknown rock she’s found. This rock is attached to the same spring, which is now attached to the wall of the spacecraft. The mass is disturbed from equilibrium and the period of the resulting oscillations is found to be 2 s. What is the ratio of the mass of the new rock to the mass of the rock found on Earth?
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Astronomy:
6.What is a brown dwarf? Is it different from a proto-star? How?
7. What different types of gas do astronomers find in the interstellar medium?
8. Astronomers believe the Sun formed with other stars near the Orion Nebula. If that is true, why is the Sun here and not there?
9. Astronomers can tell the age of a star by the age of its cluster. How is this determined?
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An AM radio station has a frequency of 1000 kHz; it uses two identical antennas at the
same elevation, 150 m apart.
a) In what direction is the intensity maximum, considering points in a horizontal plane?
b) Calling the intensity in (a) I_{0}, determine in terms of I_{0} the intensity in directions making
angles of 30^{o}, 45^{o}, 60^{o} and 90^{o} to the direction of maximum intensity.
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77 kW is to arrive at a town over two 0.140 ? lines. Estimate how much power is saved if the voltage is stepped up from 240 V to 2400 V and then down again, rather than simply transmitting at 240 V . Assume the transformers are each 99% efficient.
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For each answer, please briefly explain the reasoning behind the answer.
1. True or False: For heat pumps, wcycle, irreversible > wcycle, reversible
2. True or False: All pure substances must have S = 0 at T = 0 K.
3. True or False: The maximum theoretical efficiency of a reversible heat engine will decrease if the working substance is a real gas instead of an ideal gas.
4. A reversible process is carried out on an ideal gas NOT under constant pressure conditions. Given that for this process ΔS > 0 and ΔH = 0,
a. the system absorbs heat and expands during the process.
b. the system absorbs heat and contracts during the process.
c. the system loses heat and expands during the process.
d. the system loses heat and contracts during the process.
e. cannot be determined from the information given.
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An infinitely long line of charge has a linear charge density of 5.50×10^{−12} C/m . A proton is at distance 15.0 cm from the line and is moving directly toward the line with speed 1100 m/s .
How close does the proton get to the line of charge?
Express your answer in meters.
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A red car and a blue car are driving in the same direction on the interstate. The red car
is travelling at 25 m/s, while the blue car is travelling at 35 m/s. The driver of the blue
car is not paying attention and rear-ends the red car. The red car has a mass of 2,000
kg while the blue car is only 1,000 kg.
a. Prior to the collision, what is the value of the center of mass kinetic energy?
b. In order for this collision to be isolated, what is the maximum amount of energy
that can be converted to other forms during the collision? What percentage of
the initial kinetic energy does this represent?
c. If the system loses 40% of its kinetic energy in the collision, is the system
isolated? Why or why not?
d. Prior to the collision, how fast and in what direction would you need to be
travelling in order for the system to appear to have zero momentum?
e. Regardless of your answer to part (c), assume now that the two vehicles form
an isolated system. If they cars stick together, how fast will they be moving?
f. What minimum amount of kinetic energy must be conserved in order for this
system to be isolated?
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4.81e+20 electrons pass through a point in an electrical circuit
every 4.96 seconds.
(a) 2080 C of charge pass through that point in how many
minutes?
(b) The current though that point is ______ A.
(c) If the resistance of the circuit is 29.3 ? across this leg of
the circuit, the voltage across this leg of the circuit is _______
V.
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Object A, which has been charged to + 16 nC , is at the origin. Object B, which has been charged to − 22 nC , is at
(x,y)=(0.0cm,2.0cm)What is the magnitude of the electric force on
object
A?
Express your answer using two significant figures.
Part B
What is the magnitude of the electric force on object B?
Part C
What is the direction of the electric force on object A?
a. | positive x-axis |
b. | positive y-axis |
c. | negative x-axis |
d. | negative y-axis |
Part D
What is the direction of the electric force on object B?
a.positive x-axis | |
b.positive y-axis | |
c. | negative x-axis |
d. | negative y-axis |
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Scientists want to place a 4 × 10^{3} kg satellite in orbit around Mars. They plan to have the satellite orbit a distance equal to 2.3 times the radius of Mars above the surface of the planet. Here is some information that will help solve this problem:
m_{mars} = 6.4191 x 10^{23} kg
r_{mars} = 3.397 x 10^{6} m
G = 6.67428 x 10^{-11} N-m^{2}/kg^{2}
1)
What is the force of attraction between Mars and the satellite?
2)
What speed should the satellite have to be in a perfectly circular orbit?
3)
How much time does it take the satellite to complete one revolution?
4)
What should the radius of the orbit be (measured from the center of Mars), if we want the satellite to take 8 times longer to complete one full revolution of its orbit?
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