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NDSU Physics Exam 3 Study Set
You are a construction worker standing still on 12th Ave N in Fargo, and you watch a minivan drive past at 25 mi/hr eastward. A kid in the back throws a ball at his brother in the front seat at 16 mi/hr. How fast does the ball move, as observed by you? (Positive indicates east, negative indicates west.) - Answer 25 mi/hr + 16 mi/hr
= 41 mi/hr
How fast does the ball move, according to the kid who threw it? - Answer 16 mi/hr
If instead, the kid in the front seat throws a rock at the kid in the back seat at 16 mi/hr, how fast would you observe the rock to travel? - Answer 25 mi/hr - 16 mi/hr
= 9 mi/hr
When you are enclosed in a box, is there any way you can tell if you are moving, and if so, how fast you are going? - Answer There is nothing I could do to determine my speed.
You are driving northward on Interstate-29 at 35 mi/hr, and a sports car (also traveling northward) passes you at 82 mi/hr. What is the velocity of the sports car, relative to you? (Indicate northward as positive, and southward as negative.) - Answer 82 mi/hr - 35 mi/hr
=47 mi/hr
We often think we are motionless, but our planet is actually revolving around the sun (and rotating on its axis). What is the orbital speed of Earth moving around the sun? Recall that the average distance between Earth and the sun is 1.5 x 1011 m, and the time required for a revolution is about 365 days. (Hint: Assume Earth's orbit is a perfect circle; then a formula from geometry will allow you to find the total distance Earth moves in a year.) - Answer 3.0×10^4 m/s
What is the velocity of your car, relative to the other driver?(Indicate northward as positive, and southward as negative.) - Answer 35 mi/hr - 82 mi/hr
-47 mi/hr
The Rebel spaceship "Home One" is traveling through space at 30,000 km/s. Admiral Ackbar shines a green laser pointer towards the front of the spaceship. How fast does the laser light move relative to him? - Answer 3.0×10^8 m/s (speed of light)
If Chewbacca is on a stationary space station watching "Home One" move past, how fast does the laser light move according to him? - Answer 3.0×10^8 m/s (speed of light)
Classify the following as True or False To an observer at rest - Answer True: To an observer at rest, a fast-moving spaceship appears to possess more inertia than when it's at rest.
True: To an observer at rest, a person in a fast-moving spaceship appears to age slower.
True: To an observer at rest, the clocks of a fast-moving spaceship appear to run slow.
Mario is watching Luigi fly past in a spaceship at 2.26×108 m/s. How long does it take for one hour to pass for Luigi, according to Mario? - Answer t = ts / square root (1 - v^2/c^2)
t = 1 hr / square root (1 - 2.26E8^2/3E8^2)
t = 1.52 hr
How long does an hour on the ship last, according to Luigi? - Answer 1 hr
How long does an hour last for Mario, according to Luigi? - Answer t = ts / square root (
t = 1 hr / square root (1 - 2.26E8^2/3E8^2)
t = 1.52 hr
You are standing still and watching a spaceship fly past. You observe that it takes 1.7 hr for the clocks on the spaceship to advance by 1.0 hr. How fast is the spaceship moving, relative to you? - Answer t = ts / square root (1 - v^2/c^2)
V = c x square root (1 - ts/t)
V = 3E8 x square root (1 - 1 hr / 1.7 hr)
V = 2.4E8 m/s
Jane Jetson decides to get a divorce from George. As part of the settlement, she gets the dog, Astro. She flies her spaceship past George at 91% of the speed of light. If Astro was 15 years old when she left, and Jane observes that Astro lives for 3 more years on the ship, how old does George observe Astro to be when the dog passes away? - Answer t = ts / square root (1 - v^2/c^2)
t = 3 / square root (1 - (91%)^2)
t = 7.24 yr
15 yr + 7.24 yr = 22.2 yr
How old does Jane say that Astro is when he dies? - Answer 15 yr + 3 yr
18 yr
Luke and Leia are twins, and Luke immediately leaves after birth on a spaceship traveling at 65% of the speed of light, and he remains traveling at this speed until he returns to his sister. When Luke returns, Leia is 14 years old. How old is Luke when he returns? - Answer t = ts / square root (1 - v^2/c^2)
operates by splitting uranium, how much uranium rest-mass is converted to energy in a day? (For simplicity, assume the power plant is 100% efficient.) - Answer E = mc^
m = E / c^
m = (2.5E9 w) (24 hr x 60 min x 60 sec) / 3E8^
m = 2.4E-3 kg
What is the main idea of general relativity? - Answer Gravity and acceleration are two equivalent concepts and one can be transformed into the other.
What is the main advantage of the general theory of relativity over the special theory of relativity? - Answer General relativity applies to all observers, while special relativity applies only to nonaccelerated observers.
A man has a mass of 74.8 kg. What is his weight on Earth? - Answer F = mg
F = 74.8 kg x 9.8 m/s^
F = 733 N
What would he observe his weight to be if he is accelerating vertically in a spaceship at 3g, far from all gravitational influences? - Answer F = mg
F = 74.8 kg x(3 x 9.8 m/s^2)
F = 2.2E3 N
What does it mean when we say that space is curved? - Answer The sum of all three angles in a triangle will not add up to 180 degrees
A light beam will appear to bend the most near: - Answer a star with twice the mass of our sun.
According to an observer on Earth, a person orbiting close to a black hole would appear to: - Answer age slowly
Classify the following as True or False based on the Big Bang - Answer True: Most galaxies appear to be moving away from one another.
True: As space expands, the wavelength of the cosmic background radiation increases.
Why do we believe that the universe started in a "big bang"? - Answer All galaxies are observed to move apart, so that they should all have come from a single origin some time in the past.
What did the universe consist of at the time the microwave background radiation originated? - Answer Nearly uniformly distributed hydrogen and helium atoms and radiation.
When we say the universe is flat, we mean: - Answer True: the angles of a triangle drawn across a large portion of the universe would add up to 180°.
True: the universe has no overall large-scale curvature.
If you point a telescope into the sky, could you directly observe dark matter? Could you indirectly observe it? - Answer No, because dark matter does not interact with electromagnetic radiation. Yes, you could observe its gravitational effects on stars and galaxies.
Why did Physicists propose the existence of Dark Energy, and how important is it supposed to be? - Answer The expansion of the universe should be slowing down, but it has been shown to be accelerating. Dark energy is the energy that has been proposed to fuel this acceleration. If this proposed dark energy exists it would make up the majority of the universe according to E=mc2.
Rank the following according to their abundance in the universe, where #1 is the most abundant and #4 is the least abundant. - Answer 1: Dark Energy
2: Dark Matter
3: Ordinary Nonluminous Matter
4: Ordinary Luminous (Visible) Matter
Pick the best term corresponding to each statement.
Dark Matter / Dark Energy / ordinary visible matter / Intergalactic Gas - Answer Dark Matter: This is believed to exist to explain what holds galaxies together.
Dark Matter: This interacts through the gravitational force but is not made of protons, neutrons, or electrons.
Dark Energy: This is believed to exist to explain the accelerating expansion of the universe.
Ordinary Visible Matter: This is what stars are made of.
In the double-slit experiment with light, when the light is between the slits and the screen, it is best described as ____________________; when it impacts the screen, it is best described as _________________. - Answer an electromagnetic wave (field); a particle (photon)
An electromagnetic field carries radiation of frequency 4.26×1014 Hz. Which of the following is a possible energy for the field? - Answer E = h x f
E = 6.6e-34 x 4.26×1014 Hz
E = 2.81e-19 (not an option)
E = 6.6e-34 x 4.26×1014 Hz x 2 particles
E = 5.62e-19 (correct option)
Rank the following photons by energy, where 1 is the most energetic and 6 is the least energetic. - Answer 1: Gamma photon
2: X-ray photon
3: Ultraviolet photon
4: Blue photon
5: Red photon
6: Radio photon
What is the energy of a photon with a frequency of 99.3 MHz? - Answer E = h x f
E = 6.6e-34 x (99.3 MHz x 1000000)
E = 6.6e-26 J
What is the energy of a photon of wavelength 106 nm? - Answer f = c / λ E = h x f
E = h x (c / λ)
E = 6.6e-34 x (3.0e8 / 1.06e-7 m)
E = 1.9e-18 J
A light source emits light of frequency 4.3×1014 Hz at a rate of 7.1 J per second. How many photons are emitted per second by this source? (No units required.) - Answer Number of photons? = E / f ???
= 7.1 J / sec / 4.3e14 Hz
= 2.5e
What is the wavelength of a dust particle of mass 9.8×10-9 kg and speed 19.0 m/s? - Answer λ = h / (m x v)
λ = 6.6e-34 / (9.8e-9 kg x 19 m/s)
λ = 3.5e-27 m
Suppose that a certain electron has twice the velocity of a certain proton. Which one has the shorter wavelength? - Answer The proton, due to its much larger mass.
In the double-slit experiment with electrons, the location of each individual electron impact is _____________, while the overall interference pattern is _____________. - Answer uncertain; predictable
What is the smallest nonzero energy that an electron's matter field can have? (Recall that the mass of an electron is 9.11 x 10-31 kg.) - Answer E = m x c^
E = 9.11e-31 kg x 3.0e8^
E = 8.2e-14 J
50,000 electrons are shot through a double-slit experiment apparatus. 20,000 of them are detected in the central bright band, 10,000 of them are detected in each of the bands adjacent to the central band, and 5,000 of them are detected in each of the next two bands out from the central band. What is the probability that the next electron will be detected in the central band? - Answer Central bright Band / total electrons
20,000 / 50,000 = 0.
40% probability
