# qwerty

Popular questions and responses by qwerty-
## Astronomy

A roughly spherical asteroid with a diameter of 1 km, and a mean density of 4 g/cm^3, hits the Earth with a relative speed 1.5 times the orbital velocity of the Earth. Compute the amount of energy released upon the impact. Compare that with the energy

*asked on April 25, 2014* -
## Chemistry

1)Buttermilk has 9 grams of protein and 12 grams of carbohydrate per cup (237ml). Estimate the concentration in mol/L of protein using the fact that the average protein is 300 amino acids long and the average amino acid has a mass of 110 amu. 2)Lactose

*asked on October 10, 2013* -
## Chemistry

The following questions concern the iconic Nestle Toll House Chocolate Chip Cookie recipe, shown below: 2 1/4 cups all-purpose flour 1 teaspoon baking soda 1 teaspoon salt 1 cup butter or margarine, softened 3/4 cup granulated sugar 3/4 cup packed brown

*asked on October 10, 2013* -
## Quantum Physics

What is the maximum value of the wavelength of light that will ionize the hydrogen atom? Express your answer in units of nanometers.

*asked on April 22, 2013* -
## Materials Science

A cylindrical pressure vessel, with a diameter of 40cm and a wall thickness of 10mm is made of steel (isotropic, with Young’s modulus = 200GPa; Poisson’s ratio = 0.28) and is pressurized to 20MPa. The longitudinal and hoop stresses in the wall, σl and

*asked on October 1, 2014* -
## Material Sciences

Given an aluminum shell perfectly bonded to a steel core, what is the thermal stress in the aluminum shell when the system is heated from the unstressed state (20∘C) to 180∘C? Consider only deformations in the axial directions. Give your answer in MPa

*asked on September 27, 2014* -
## Statics

A cantilever beam, made of a material with a Young's modulus, E with a rectangular cross section with a moment of inertia I, is under a uniformly distributed load, q, across the length L of the cantilever at a point load P at the free end of the

*asked on October 23, 2014* -
## Materials Science

Aluminum is a cubic crystal, with S11=1.59×10−11 m2/N S12=−0.58×10−11 m2/N S44=3.52×10−11 m2/N What are the Young's modulus, Poisson's ratio and shear modulus, corresponding to these values? Young's modulus E (in GPa): Poisson's ratio ν: Shear

*asked on October 1, 2014* -
## Chemistry

For each of the following, enter the number of covalent bonds that the atom can form: (A) One atom of carbon (B) One atom of sulfur (C) One atom of nitrogen with no net charge (D) One atom of nitrogen with positive net charge (E) One atom of oxygen with no

*asked on March 7, 2013* -
## Probability

Each one of n persons, indexed by 1,2,…,n, has a clean hat and throws it into a box. The persons then pick hats from the box, at random. Every assignment of the hats to the persons is equally likely. In an equivalent model, each person picks a hat, one

*asked on February 20, 2015* -
## Statics

Calculate the elastic buckling collapse stress (the compressive strength), σ∗el, for an open-cell polystyrene foam with a relative density of 0.1. (Es for polystyrene = 3.5GPa). Recall that C2=0.05. Give the results in MPa. σ∗el (in MPa): The energy

*asked on October 23, 2014* -
## Materials Science

Calculate the ratio of the moments of inertia I1I2 of two beams of rectangular cross section of the same width, one with a height h and the other, made up of three thinner beams of height h/3. I1/I2 = ?

*asked on October 16, 2014* -
## Materials Science

A cube of the isotropic, linear elastic epoxy resin E=2GPa, ν=0.3, α=50×10−6K−1 at 20∘C is unloaded. It is then heated to 60∘C. What is the corresponding strain matrix? The temperature is held constant at 60∘C. What stress is required to

*asked on October 1, 2014* -
## Materials Science

A linear elastic, isotropic epoxy resin with elastic modulus, E=2GPa, and Poisson’s ratio, ν=0.3, is loaded by the following stress state: σ=⎡⎣10 5 0 5 −20 0 0 0 0⎤⎦MPa Give numerical values for all strain components in the corresponding

*asked on October 1, 2014* -
## Astronomy

The star Polaris has a surface temperature of roughly 6500 K and a radius of approximately 50 solar radii. Find the luminosity of Polaris in terms of the Sun's luminosity.

*asked on June 24, 2014* -
## Astronomy

A quasar is observed at a redshift of z=1, which corresponds to a comoving radial distance of 3 Gpc. Its observed bolometric flux is 10^{-12} erg/cm^2/s. An interacting companion galaxy is seen 4 arcsec apart in projection. What is the bolometric

*asked on June 19, 2014* -
## Materials Science

Rubber particles, roughly 1mm in diameter, have been added to an epoxy resin to increase its resistance to crack growth. Estimate the Young's modulus of the composite, given that the Young's moduli of the epoxy and the rubber are, respectively, 2GPa and

*asked on October 1, 2014* -
## Material Sciences

The molar crosslink density of a rubber is measured to be 468mol/m3 for a temperature T=300K. What is the Young's modulus of the rubber in MPa? What happens to the modulus of the rubber when the temperature is increased? Young's modulus decreases Young's

*asked on September 28, 2014* -
## Chemistry

The units of parts per million (ppm) and parts per billion (ppb) are commonly used by environmental chemists. In general, 1 ppm means 1 part of solute for every 106 parts of solution. (Both solute and solution are measured using the same units.)

*asked on January 23, 2019* -
## Statics

Four identical pin-pin ended solid concrete cylindrical columns that are L=10m tall need to be able to withstand 6.8×108N of force before Euler buckling. What should be the diameter, d, in meters, of each column if the force is uniformly distributed? The

*asked on October 23, 2014* -
## Statics

A rectangular beam, with cross-sectional width b, height h, Young's modulus Erect, has the same flexural rigidity as a circular beam with the same cross-sectional area. What is the Young's modulus, Ecirc, of the circular beam in terms of Erect,b, and h?

*asked on October 23, 2014* -
## Quantum Physics

Suppose we ran m steps of Grover's algorithm on some function f (which has one marked element y) and the resulting superposition was exactly |y⟩. If we run for m+1 additional steps (i.e. total of 2m+1 steps from the initial state), what is the resulting

*asked on April 16, 2013* -
## Statics

You have 1kg of aluminum (E=69GPa) to make a cylindrical tube with a high Euler buckling load. The tube must have a length L of 0.5m. You can either make a solid tube, or a thin walled tube with a wall thickness, t=0.5cm. The density of aluminum is

*asked on October 23, 2014* -
## Material Sciences

The boron fibers are produced by chemical vapor deposition of boron onto fine tungsten wires of dW=10μm. The final wire diameter is dB=75μm. The boron coated wires are then added to an aluminum matrix with VW+B=0.35 fiber volume fraction. The Youngs

*asked on September 20, 2014* -
## Quantum Physics

- What is QFT6 of 1/√2(|0> + |3>? - What is QFT6 of 1/√2(|1> + |4>? - What is QFT6 of 1/√3(|0> + |2> + |4>? - What is QFT6 of 1/√3(|1> + |3> + |5>?

*asked on March 20, 2013* -
## material science, math

Calculate the ratio of the moments of inertia I1/I2 of two beams of rectangular cross section of the same width, one with a height h and the other, made up of three thinner beams of height h/3. I1/I2 = ?

*asked on October 21, 2015* -
## Statics

You have a stainless steel hollow rod (E=193GPa,ν=0.29) that has an inner radius r of 1.2cm, a wall thickness t of 0.7mm, and a length L of 5cm. Calculate the critical loads, in kN, for local buckling and Euler bucking (Pcr,local and Pcr,Euler,

*asked on October 23, 2014* -
## Materials Science

A hollow cylinder with outer radius r0 and inner radius ri is loaded by a uniformly distributed load q across its length L. The beam is supported by a roller at its left end and a pin L5 from its right end. What is the maximum bending moment in the beam?

*asked on October 17, 2014* -
## Materials Science

A 3-point bending test is performed on a simply supported beam of length L=4m and of rectangular cross-section, with width b and height h. For a central load of 10kN, draw the bending moment and shear force diagrams for the beam. Then answer the following

*asked on October 17, 2014* -
## Big Data

Suppose our input data to a map-reduce operation consists of integer values (the keys are not important). The map function takes an integer i and produces the list of pairs (p,i) such that p is a prime divisor of i. For example, map(12) = [(2,12), (3,12)].

*asked on October 6, 2014* -
## Probability

Before leaving for work, Victor checks the weather report in order to decide whether to carry an umbrella. On any given day, with probability 0.2 the forecast is “rain" and with probability 0.8 the forecast is “no rain". If the forecast is “rain",

*asked on February 13, 2015* -
## Logic

Consider a propositional language with three propositional constants - mushroom, purple, and poisonous - each indicating the property suggested by its spelling. Using these propositional constants, encode the following English sentences as Propositional

*asked on October 6, 2014* -
## Material Sciences

Imagine a container is removed from a hot oven and plunged into cold water. Use your answer from Question 3 to justify which material would be more likely to have better thermal shock resistance. Glass: α=9∗10−6C−1 Pyrex: α=4∗10−6C−1 Which

*asked on September 28, 2014* -
## Material Sciences

A steel bar of length L and cross-sectional area A is fitted between rigid supports. Write an expression for the stress in the bar when the temperature is raised by an amount ΔT. Write your answer in terms of α,E and ΔT. Is the stress compressive or

*asked on September 27, 2014* -
## Material Sciences

A unidriectional, continuously reinforced glass fiber composite has Vf=60 volume percent fibers in a matrix of epoxy. Glass has a Young's Modulus of Eglass=70GPa; epoxy has a Young's Modulus of Eepoxy=2GPa (a) Give numerical values for (i) the Young's

*asked on September 20, 2014* -
## Probability

Alice plays the following game with Bob. First, Alice randomly chooses a set of 4 cards out of a 52-card deck, memorizes them, and places them back into the deck. (Any set of 4 cards is equally likely.) Then, Bob randomly chooses 8 cards out of the same

*asked on February 23, 2014* -
## Statics

Compare the Young's modulus E∗ of two open-cell foams. Which Young's modulus is higher? Recall that C1=1. 1. polystyrene: (Es∼3.5GPa), ρ∗/ρs=0.3 2. Al 7075-T651: (Es∼72GPa), ρ∗/ρs=0.1 E∗PS (in GPa): E∗Al (in GPa): Select the correct

*asked on October 23, 2014* -
## Astronomy

The current peak wavelength of the CMB corresponds to a blackbody of temperature 2.74K. What was the peak wavelength of the CMB when it was emitted? The current redshift of the CMB is z=1100. Give your answer in microns. Which waveband regime is this?

*asked on June 24, 2014* -
## Astronomy

Imagine that you have found an object out in space. When you use the inverse square law to compute its luminosity, you get a ridiculously large value. You therefore suspect that relativistic beaming is at work - the radiation is coming from a jet traveling

*asked on May 11, 2014* -
## Quantum Physics

Consider a particle whose wavefunction at some fixed time t is represented by -A if -2≤x≤0 ψ(x)= A if 0≤x≤3 0 otherwise (a) What is the normalization constant A? (b) What is the probability of finding the particle at a position x≤0? (c) What is

*asked on April 6, 2013* -
## Probability

You roll two five-sided dice. The sides of each die are numbered from 1 to 5. The dice are “fair" (all sides are equally likely), and the two die rolls are independent. Part (a): Event A is “the total is 10" (i.e., the sum of the results of the two die

*asked on February 13, 2015* -
## Mechanical Behavior of Materials

What is the exact strain energy per unit length of an edge dislocation for a material that has a Young's modulus E of 50GPa, a Burger's vector b of 0.25nm, a dislocation density ρ of 108cm−2, and a Poisson's ratio ν of 0.3? Uedge (in J/m): What is the

*asked on November 23, 2014* -
## Astronomy

Imagine that you are an astronomer, and you are planning to do a survey to find new brown-dwarf stars. You need to calculate how sensitive your search needs to be (and hence how big a telescope you will need and how long the survey will take). You want to

*asked on May 11, 2014* -
## Probability

You are given the set of letters ( A, B, C, D, E ). What is the probability that in a random five-letter string (in which each letter appears exactly once, and with all such strings equally likely) the letters A and B are next to each other?

*asked on February 23, 2014* -
## History

Civilizations of the Americas Practice 1. Which of the following statements explains why the Aztec continually waged war? A. The Aztec needed prisoners of war to work the land. B. The Aztec needed more people to help build their pyramids. C. The Aztec

*asked on April 14, 2019* -
## Probability

The newest invention is a three-sided die. On any roll of this die, the result is 1 with probability 1/2, 2 with probability 1/4, and 3 with probability 1/4. Consider a sequence of six independent rolls of this die. 1. Find the probability that exactly two

*asked on February 23, 2014* -
## Probability

A fair, 6-sided die is rolled 6 times independently. Assume that the results of the different rolls are independent. Let (a1,…,a6) denote a typical outcome, where each ai belongs to {1,…,6}. Find the probability that the results of the 6 rolls are all

*asked on March 7, 2015* -
## Quantum Physics

Consider the observable M that corresponds to a measurement in the sign basis where the measurement value is 3 if the outcome is + and -2 if the outcome is - A)Write M in the standard basis. B)If M is the Hamiltonian acting on a qubit which is in the state

*asked on April 16, 2013* -
## Quantum Physics

Suppose H|ψ> = 1/√2 (|000> + |111>). What is |ψ> ? Specify the probability amplitude for each component: |000> = |001> = |010> = |011> = |100> = |101> = |110> = |111> =

*asked on March 3, 2013* -
## Probability

Consider the communication network shown in the figure below and suppose that each link can fail with probability p. Assume that failures of different links are independent. Assume that p=1/3. Find the probability that there exists a path from A to B along

*asked on February 16, 2015* -
## Probability

Oscar has lost his dog in either forest A (with probability 0.4) or in forest B (with probability 0.6). If the dog is in forest A and Oscar spends a day searching for it in forest A, the conditional probability that he will find the dog that day is 0.25.

*asked on February 13, 2015* -
## Mechanical Behavior of Materials

A material has a Young's modulus E of 50GPa, a Burger's vector b of 0.25nm, and a Poisson's ratio ν of 0.3. What is the approximate line tension for a dislocation in this material?

*asked on November 23, 2014* -
## Materials Science

A 4-point bending test is performed on the same beam, with symmetric loads of 5kN separated by 2m. Draw the bending moment and shear force diagrams for the beam. Then answer the following questions about the shear force V and bending moment M. What is the

*asked on October 17, 2014* -
## Astronomy

Rank the following hypothetical planets -- all of which have the same total mass and same radius -- from lowest moment of inertia to highest moment of inertia: 1) A uniform sphere of mixed up rock and iron 2) A hollow sphere 3) A rocky planet with an iron

*asked on April 21, 2014* -
## Probability

A player is randomly dealt a sequence of 13 cards from a standard 52-card deck. All sequences of 13 cards are equally likely. In an equivalent model, the cards are chosen and dealt one at a time. When choosing a card, the dealer is equally likely to pick

*asked on February 23, 2014* -
## Quantum Physics

The ground state wavefunction for a particle in a shallow potential well in 1 dimension is of the form: Ae^(−|x|/2d). Given that the particle must be found somewhere in the range x∈[−∞,∞], the born rule then places a constraint on the modulus of

*asked on April 3, 2013* -
## Biology

Dopamine is a neurotransmitter—a chemical released by nerve cells to send signals to other nerve cells. Activities like sex and gambling increase the levels of dopamine released within the brain. The highly addictive drugs cocaine and methamphetamine

*asked on March 7, 2013* -
## Chemistry

An equilibrium mixture contains 0.250 mol of each of the products (carbon dioxide and hydrogen gas) and 0.200 mol of each of the reactants (carbon monoxide and water vapor) in a 1.00-L container. CO(g) + H2O(g) CO2(g)+ H2(g) How many moles of carbon

*asked on March 3, 2013* -
## Quantum Physics

We have a qubit in the state |ψ>= √3/2 |0>+ 1/2 |1>, which we want to measure in the {Cos θ |0> + Sin θ |1>, Sin θ |0> - Cos θ |1>} basis. In order for the two possible outcomes to be equiprobable, what should be the value of θ in degrees? (Answer

*asked on February 12, 2013* -
## Algebra

You borrow $40 from your sister. To repay the loan, you pay her $5 a week. Write a linear equation to model the situation and check with unit alalysis.

*asked on November 13, 2011* -
## math

A hollow cylinder with outer radius r0 and inner radius ri is loaded by a uniformly distributed load q across its length L. The beam is supported by a roller at its left end and a pin L5 from its right end. What is the maximum bending moment in the beam?

*asked on October 24, 2015* -
## math, mechanics

Calculate the ratio of the moments of inertia I1/I2 of two beams of rectangular cross section of the same width, one with a height h and the other, made up of three thinner beams of height h/3.

*asked on October 23, 2015* -
## Probability

Consider a sequence of independent tosses of a biased coin at times k=0,1,2,…,n. On each toss, the probability of Heads is p, and the probability of Tails is 1−p. A reward of one unit is given at time k, for k∈{1,2,…,n}, if the toss at time k

*asked on February 25, 2015* -
## Logic

Use Propositional Resolution to show that the clauses {p, q}, {¬p, r}, {¬p, ¬r}, {p, ¬q} are not simultaneously satisfiable. Proof takes 8 steps including the premises and the goal.

*asked on October 23, 2014* -
## Materials Science

At a point in a plate subjected to plane stress loading along its surface, the cartesian stress components acting on the x-face of an element oriented along the (x,y) frame are σx=40MPa and τxy=70MPa, The maximum allowable shear stress, to prevent

*asked on October 10, 2014* -
## Astronomy

A galaxy is receding away from us with a recession velocity of 100,000 km/s. What is the distance to this galaxy? What is the redshift z of this galaxy?

*asked on June 24, 2014* -
## Probability

In parts 1, 3, 4, and 5 below, your answers will be algebraic expressions. Enter 'lambda' for and 'mu' for . Follow standard notation. 1. Shuttles bound for Boston depart from New York every hour on the hour (e.g., at exactly one o'clock, two o'clock,

*asked on April 29, 2014* -
## Astronomy

Which of the following statements is correct? (check all that apply) If liquid water is not stable on the surface of Mars, liquid CO2 is definitely not stable. If liquid CO2 is not stable on the surface of Mars, liquid water is definitely not stable. If

*asked on April 21, 2014* -
## Probability

Random variables X and Y are distributed according to the joint PDF fX,Y(x,y) = {ax,0,if 1≤x≤2 and 0≤y≤x,otherwise.} 1. Find the constant a. 2. Determine the marginal PDF fY(y). (Your answer can be either numerical or algebraic functions of y). For

*asked on March 18, 2014* -
## Astronomy

The coolest star whose peak blackbody wavelength can be observed with the human eye (the exact range of visible light varies from publication to publication, so use 380nm to 750 nm).

*asked on March 4, 2014* -
## Biochemistry

Amylase is secreted by your pancreas into your small intestine where amylase helps you digest the starches in your diet. Amylase does this because it is an enzyme, a protein that catalyzes a chemical reaction. In this case, amylase catalyzes the breakdown,

*asked on March 30, 2013* -
## Quantum Physics

Suppose we are given a single qubit which is either in the state |u> = cos(pi/8) |0> + sin(pi/8) |1> or |v> = cos(3pi/8) |0> + sin(3pi/8) |1>. We measure this qubit in the standard basis and guess u if the outcome is 0 and guess v if the outcome is 1. (a)

*asked on March 11, 2013* -
## Astronomy

Which type of emission closely traces the star-forming regions of a galaxy? - molecular CO emission - coronal X-ray emission - 21 cm emission - none of these

*asked on March 1, 2013* -
## history

compare and contrast two ancient civilizations. i had the choice between -indus -mesoamerica -egypt -mesopotamia -china haung he river i think im going to write about egypt and mesopotamia since they have alot on them... for now all i have to write is an

*asked on September 18, 2008* -
## geography

which of the following was NOT a characteristic of native american societies during the mississippian period

*asked on October 16, 2019* -
## Physics

I want to become an astonomer or study astrophysics but I didnt do maths a level can I still do it? Is there any way you can help me or provide aN alternative

*asked on October 5, 2017* -
## Probability

A dedicated professor has been holding infinitely long office hours. Undergraduate students arrive according to a Poisson process at a rate of λu=3 per hour, while graduate students arrive according to a second, independent Poisson process at a rate of

*asked on May 26, 2015* -
## Probability

Let θ be an unknown constant. Let W1,…,Wn be independent exponential random variables each with parameter 1. Let Xi=θ+Wi. What is the maximum likelihood estimate of θ based on a single observation X1=x1? Enter your answer in terms of x1 (enter as x_1)

*asked on May 26, 2015* -
## Probability

Let X and Y be independent random variables, each uniformly distributed on the interval [0,2]. Find the mean and variance of XY. E[XY]= - unanswered var[XY]= - unanswered Find the probability that XY≥1. Enter a numerical answer. P(XY≥1)= - unanswered

*asked on May 26, 2015* -
## Probability

A fair coin is tossed repeatedly and independently. We want to determine the expected number of tosses until we first observe Tails immediately preceded by Heads. To do so, we define a Markov chain with four states, {!@#$%^&,HT}, where S is a starting

*asked on May 19, 2015* -
## Probability

Let U, V, and W be independent standard normal random variables (that is, independent normal random variables, each with mean 0 and variance 1), and let X=3U+4V and Y=U+W. Give a numerical answer for each part below. You may want to refer to the standard

*asked on April 21, 2015* -
## Probability

Let A,B,C be three events and let X=IA, Y=IB, Z=IC be the associated indicator random variables. We already know that X⋅Y is the indicator random variable of the event A∩B. In the same spirit, give an algebraic expression, involving X, Y, Z for the

*asked on March 7, 2015* -
## Probability

The newest invention of the 6.041x staff is a three-sided die. On any roll of this die, the result is 1 with probability 1/2, 2 with probability 1/4, and 3 with probability 1/4. Consider a sequence of six independent rolls of this die. 1. Find the

*asked on February 20, 2015* -
## Logic

Given the premises (p ⇒ q) and (r ⇒ s), use Propositional Resolution to prove the conclusion (p ∨ r ⇒ q ∨ s). Proof takes 8 steps including the premises and the goal.

*asked on October 23, 2014* -
## Materials Science

A 3m long balance beam is simply supported with an overhang at each end of a=0.5m. A gymnast weighing 50kg is standing a distance c to the right of support A and a distance b to the left of support B. How does the maximum bending moment in the beam depend

*asked on October 16, 2014* -
## Materials Science

In this problem, you will construct the 2D Mohr's circle for two plane stress states defined in terms of the Cartesian components of the stress tensor in the x,y reference frame: [ σx,σy,τxy]. For each of these stress states, you must construct and use

*asked on October 10, 2014* -
## Algorithms

Arrange the following functions in increasing order of growth rate (with g(n) following f(n) in your list if and only if f(n)=O(g(n))). a)2^2^n b)2^n^2 c)n^2 * log(n) d)n e)n^2^n

*asked on October 9, 2014* -
## Physics

Which of the following processes is used in order to fabricate monocrystalline silicon? Note that more than one correct answer is possible. The Czochralski process Silicon ribbon process The float-zone process The silicon casting process

*asked on October 8, 2014* -
## Physics

Let's assume that solar light reaches a silicon solar cell with an angle of incidence of θi=0o. For simplicity, let's consider the refractive index of silicon to be nSi=3.5. The refractive index of air is nair=1. What percentage of light would be lost due

*asked on October 3, 2014* -
## Physics

A solar cell with dimensions 12cm x 12cm is illuminated at standard test conditions. The cell presents the following external parameters: Voc=0.8V,Isc=3A,Vmp=0.75V,Imp=2.5A Calculate the fill factor in percentage [%]: Calculate the efficiency (in %):

*asked on October 3, 2014* -
## Physics

The current density of an ideal p-n junction under illumination can be described by: J(V)=Jph−J0(e^qV/kT−1) where Jph is the photocurrent density, J0 the saturation current density, q the elementary charge, V the voltage, k the Boltzmann's constant,

*asked on October 3, 2014* -
## Physics

The width of the space charge region at a p-n junction is reduced by applying a voltage bias over the p-n junction. What is the correct statement on both the bias voltage and the p-n junction? The voltage is a forward bias and the diffusion of the majority

*asked on October 3, 2014* -
## Materials Science

An isotropic epoxy resin (E=2GPa, ν=0.3) is reinforced by unidirectional glass fibers (Eglass=70GPa), aligned in the 2 direction, such that the fiber composite is transversely isotropic, with the 1-3 plane being the plane of isotropy. The elastic

*asked on October 1, 2014* -
## Material Sciences

The energy-separation curve for two atoms, a distance, r, apart is: U(r)=−A/r^m+B/r^n Derive and expression for the stiffness of the bond at the equilibrium spacing, in terms of A, B, m, n, and r0. S=dF/dr at r=r0:

*asked on September 27, 2014* -
## Acoustic

Consider a room that is 6m long, 5m wide and 3m high and whose walls, floor and ceiling have the same sound absorption coefficient (α=0.01). When all machines are in use, the sound pressure level (SPL) within the room amounts to 90 dB. A carpet is to be

*asked on September 11, 2014* -
## Acoustic

A breathing sphere of radius 0.1m radiates spherical waves into air at 100Hz with an intensity of 200mW/m2 at the distance 0.5m from the center of the sphere. In this case, 1) Compute the radiated acoustic power. 2) Compute the intensity at the surface of

*asked on September 11, 2014* -
## Astronomy

Supernovae can eject material at velocities of 0.001c. Will gas ejected by a supernova which occurs inside a dwarf galaxy with a mass of 10^8 Msolar and a radius of a few kpc be able to escape the galaxy? Yes or No

*asked on June 24, 2014* -
## Astronomy

The luminosity of the Sun is 4*10^33 erg/s, and its radius is 7*10^10 cm. What is the Sun's effective temperature? Please enter your answer in units of Kelvin.

*asked on May 6, 2014* -
## Astronomy

Imagine you are in a spaceship one million km from a black hole of mass kg. Initially you are flying directly away from it at a velocity of 16.9 km/s. Using the n-body approximation, what is your velocity one second later? Type your answer in metres per

*asked on May 4, 2014* -
## Astronomy

The luminosity of the Sun is 4*10^33 erg/s, and its radius is 7*10^10 cm. What is the Sun's effective temperature? Please enter your answer in units of Kelvin. What is the Sun's effective temperature? Please enter your answer in units of Kelvin. -

*asked on April 29, 2014*