Homework Definition and 998 Threads

Homework, or a homework assignment, is a set of tasks assigned to students by their teachers to be completed outside the classroom. Common homework assignments may include required reading, a writing or typing project, mathematical exercises to be completed, information to be reviewed before a test, or other skills to be practiced.
The effects of homework are debated. Generally speaking, homework does not improve academic performance among young children, because children need more sleep to develop and grow. Homework may improve academic skills among older students, especially lower-achieving students. However, homework also creates stress for students and parents, and reduces the amount of time that students can spend in other activities.

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  1. andrewkirk

    Should Forums Reinstate the Solved Tag to Improve User Experience?

    The lack of an ability to mark homework threads solved when they are is a discouragement to would-be homework helpers. Sometimes I browse for problems needing help but give up after looking at a few threads only to find that they are solved and no longer in need of input. There are some closed...
  2. A

    Solving Homework: Speed of Mass on Wagon

    Homework Statement There is a wagon (W) on wheels with a vertical pole of 2m. (mass 20kg) On the top of that pole there is a rope pendulum with an attached mass (M) of 10kg and length 1m. The starting position is a pendulum angle of 60°. No friction taken into account. What is the speed of the...
  3. stacope32

    A block sliding down a ramp lab (with friction)

    Homework Statement A block of 55 g is sliding down a ramp of 35 degrees of inclination. The hypotenuse of the ramp is 63 cm and the height is 36 cm. vi = 0 as the block starts at rest. Homework Equations vf = vi + a(t) d = vi*t + (a(t)^2)/2 kinetic energy = (mv^2)/2 The Attempt at a Solution...
  4. M

    Car-Truck Collision: Initial Common Velocity

    Homework Statement A car with a mass of 1400 kg is westbound at 50 km/h. It collides at an intersection with a northbound truck having a mass of 2000 kg and traveling at 40 km/h. What is the initial common velocity of the car and truck immediately after the collision if they have an...
  5. C

    Resultant of 3 vectors along the sides of an equilateral triangle

    Homework Statement Hi all, It is a homework problem, but I really don't quite understand the question. It reads- "3 forces of magnitudes 10N, 20N, and 30N acting on a point are parallel to the sides of an equilateral triangle, taken in order. Find their resultant"Homework EquationsThe Attempt...
  6. Sarah00

    Circular Motion Equation homework

    Homework Statement Homework Equations Circular Motion Equation The Attempt at a Solution I solved the problem and got the result to be 6 m/s2 but it is not one of the answers. I was pretty sure of my solution. So, are all choices wrong? F = ma mg sin 37 = ma a = g sin 37 = 6.01 m/s2
  7. C

    What Are Your Thoughts on Homework Threads?

    Does anyone else think it would be useful to know when homework has to be submitted on homework threads? It's well known that you learn more if aren't just given the answer but are led down a path that allows you to discover the answer yourself. However the latter can take many steps and if...
  8. R

    MHB Simple Algebra? This is from a 10 year olds homework

    OK, either I'm looking at this the wrong way, or this is way above what a 10 year old should be. Following are 2 equations containing A, B and C. A solution must be found that solves both equations, i.e. A, B and C are the same in each formula. Also, A, B and C must be whole numbers; C+2A=3B+2...
  9. L

    Calculating Mass in a Gas Stoichiometry Problem

    Hi all, While studying for my exam (and doing review questions) I came across a problem that I couldn't solve: 5. Zirconium metal and chlorine gas react to form zirconium (IV) chloride Zr + 2Cl2 = ZrCl4 a) What volume of chlorine gas must be used at 350 degrees Celsius and 50 kPa to produce...
  10. Hunny

    Fundamental Theorem of Calculus Problem

    1. If g(x) = ∫ f(t) dt = xln x, find f(1) The ∫ has x^2 on top and 0 on bottom. 2. g'(x) = f(x) <--FTC1 The Attempt at a Solution g'(x) = f(x) u=x^2 g'(x) = u*lnu * 2x(derivative of inner function) g'(x) = 2x(x^2)ln(x^2) f(1) = 2(1)(1^2)ln(1^2) f(1) = 0, since ln(1) = 0 I...
  11. L

    Solving Homework Problem #16ii: Log([x+y]/sqrt5)

    Homework Statement I am having problem with number 16ii) Homework Equations log([x+y]/sqrt5) The Attempt at a Solution Sorry still not used to latex So I tried this if x/y + y/x =3 then( (x^2 + y^2)/xy = 3xy x^2 + y^2 = 3xy (x-y)^2 = xy (x-y) = sqrt(xy) (x-y)(x+y) = sqrt(xy)(x+y) (x+y)...
  12. L

    What Is the Percent Yield from Aluminum to Potassium Alum?

    Here is the question: If 75.0 g of potassium alum is obtained from 5.00 g of aluminum, what is the percent yield? This is what I've done so far, but I'm not sure if it is fully correct: 5.00g Al x (1/26.98156) x (1/1) x 258.207 = 47.84882537g potassium alum Wouldn't this then be the...
  13. E

    Star Observation Calculation Homework

    Homework Statement The intensity of the Sun's radiation is about 1380 Wm-2 at Earth's distance, 1.5x1011m. Earth absorbs this radiation as a black body, and radiates its own energy back into space. a) How much Energy per second falls on the Earth's surface? (Diameter of Earth = 12800km) b)...
  14. Ayesha Shafique

    Homework help: Distance and time calculation

    1. If a cyclist travels at 9 km/hour what distance will he cover in 30 seconds?2. a) 75 m b) 7.5 m c)15 m d) 150 m3. My guess is that its 75 m.
  15. B

    Thermal expansion (Simple) (attempt posted)

    Homework Statement I'm looking for a good explanation, not interested in the answer. A geodesic dome constructed with an aluminum framework is a nearly perfect hemisphere; its diameter measures 55.0 on a winter day at a temperature of -18 C. How much more interior space does the dome have in...
  16. L

    How Should Spinors Be Applied in Physics Homework Involving Fermions?

    Homework Statement Homework EquationsThe Attempt at a Solution I've started from writing out the amplitude. Here I know that fermion has definite helicity so I can't sum over spins but I should input explicit forms of spinors. Am I correct? How to do this? I would be grateful for helping me...
  17. S

    Difficulty of undergraduate homework problems

    I am an advanced undergraduate student, and I still remember the days when I could open my mathematics textbooks, read through a few sample problems, and then blaze my way through the exercises with little or no help. Come university, and my freshman year, and things changed dramatically. I...
  18. almarpa

    Taylor Classical Mechanics example 4.9

    Hello all. I have almost finished chapter 4 on energy in Taylor's classical mechanics book. But in the last example in this chapter I got confused. Here it is: "A uniform rigid cylinder of radius R rolls without slipping down a sloping track as shown in Figure 4.23. Use energy conservation to...
  19. T

    Transfer function with Disturbance

    Homework Statement Find the steady-state error due to a disturbance Td(s) = 1/s. Set R(s) = 0. if given a system: Homework Equations n/a The Attempt at a Solution I need Y(s)/Td(s). To do this I must find Y(s) in terms of the transfer function Y(s)/R(s) which I have obtained. This gives me...
  20. R

    Lagrangian: Bead on a rotating hoop with mass

    Homework Statement 'Consider the system consisting of a bead of mass m sliding on a smooth circular wire hoop of mass 2m and radius R in a vertical plane, and the vertical plane containing the hoop is free to rotate about the vertical axis. Determine all relative equilibria of the bead.'...
  21. M

    Water Pressure Homework Problem

    Homework Statement A person swim to certain depth in the ocean where the density of sea water is 1025 kg/m3. he does not have sophisticated equipment but he used an empty tube, the tube is L = 45.4 cm long and shaped like a cylinder. He wets the sides and then puts some sand in and shakes it...
  22. leafjerky

    Solve the system using differential operators.

    Homework Statement Solve the system using differential operators. Determine the # of arbitrary constants and then compare to your solution. Homework Equations D substitution: replace x' with Dx and y' with Dy The Attempt at a Solution I have the solution to this one, but I'm working...
  23. V

    What is the final voltage that a capacitor charges towards?

    The related question says:[PLAIN]http:// The capacitor 1 is initially charged by having the flying lead attached to point C. Then, the flying lead is moved to point D. Capacitor 1 discharges. C2 has no charge intially. When the flying lead is attached to D, which one of these statements is...
  24. T

    Homework Equations: Solving for Voltage

    Homework Equations XL = ωL XC = 1/ωC Z= sqrt(R^2+(XL-XC)^2) ∅ = tan^-1(XL-XC/R) The Attempt at a Solution A) a) Irms = Vrms/R = 100 V/400 Ω = .25 A b) 1) V= Vrms =100 V 2) V = IrmsXL = IrmsωL = (.25)(1000)(.9) = 225 V 3) V= IrmsXC = Irms/ωC =...
  25. G

    Arithmetic Homework: Showing Bezout Theorem

    Homework Statement We are given ##a_1,...,a_n ## in ## \mathbb{N}^\star ##, all mutually prime, and ## a = a_1 \times ... \times a_n ##. Show that for all ##(b_1,...,b_n)\in\mathbb{Z}^n##, there is ##\beta \in \mathbb{Z} ## such that for all ##x \in \mathbb{Z} ## : ## (\forall i = 1 ... n, \...
  26. O

    Homework Question - Fundamental Theorem of Calc Example

    Homework Statement Hi, I've been working through a practice problem for which I used the fundamental theorem of calculus, or one of its corollaries. The setup is a population changing over time. The population, P(t) at t = 0 is 6 billion. The limiting population as t goes to infinity is given...
  27. D

    How Do You Calculate the Efficiency of a Heat-Transfer Process?

    Homework Statement So I am doing a mini-lab and I measured the temperature of water before heating it up and after. I determined delta T or the temperature gain to be https://www.physicsforums.com/file:///C:/Users/BADGER~1/AppData/Local/Temp/msohtmlclip1/07/clip_image002.gif...
  28. *.*.*AnUm*.*.*

    Help in Homework -- difference b/w kinematics friction and static friction?

    Hi, Please explain what is the difference b/w kinematics friction and static friction ? Please explain, what is rolling friction ? Is it when we are pulling a weight with rope, and rope is rolling on a wheel ? for example in past days, people used rope to get water from well. Please explain...
  29. U

    How do I find the scale factor of cosmological constant?

    Homework Statement (a)Sketch how the contributions change with time (b)For no cosmological constant, how long will this universe exist? (c)How far would a photon travel in this metric? (d)Find particular density ##\rho_E## and scale factor (e)How would this universe evolve?[/B] Homework...
  30. Poetria

    Moivre-Laplace theorem (homework)

    < Mentor Note -- thread moved to HH from the technical math forums, so no HH Template is shown > I have no idea what I am doing wrong. Here is my problem: S(n) - the number of successes in 10 Bernoulli trials, each with probability 0.7 I am supposed to use normal approximation to compute ...
  31. U

    Form Factor - Simply take the real part?

    Homework Statement Show that the Form factor is ##\frac{3(sin x - x cos x)}{x^3}##. Homework EquationsThe Attempt at a Solution [/B] I know that the form factor is simply the Fourier transform of the normalized charge density: F(q) = \int \frac{\rho}{Z} e^{-i (\Delta \vec k) \cdot \vec r}...
  32. U

    How do I differentiate this Scalar Field?

    Homework Statement (a) Find the christoffel symbols (Done). (b) Show that ##\phi## is a solution and find the relation between A and B.[/B] Homework EquationsThe Attempt at a Solution Part(b) \nabla_\mu \nabla^\mu \phi = 0 I suppose for a scalar field, this is simply the normal derivative...
  33. U

    Psi Meson Decay Modes: Spin, Parity, Quark Content & More

    Homework Statement (a) Explain spin and parity of mesons (b) State their quark content (c) Draw a feynman diagram of J/psi decay (d) Why doesn't ##\chi## undergo leptonic decay? (e) What is the minimum centre of mass? [/B] Homework EquationsThe Attempt at a Solution Part(a)[/B] Spin is...
  34. U

    Magnetic Susceptibility and Curie Temperature

    Homework Statement Part(a): Derive susceptibility Part(b): Find field experienced by neighbour. Part(c): State temperature range. What explains temperature dependence beyond curie temperature? Why is curie temperature so high? Part(d): In practice, measured magnetic moment is far lower than...
  35. C

    Formula for the Speed of Ocean Waves

    Homework Statement Which formula could be correct for the speed v of ocean waves in terms of the density ρ of sea-water, the acceleration of free fall g, the depth h of the ocean and the wavelength λ? The possible answers listed are: 1. v = \sqrt{gλ} 2. v = \sqrt{g/h} 3. v = \sqrt{ρgh} 4.v =...
  36. U

    What Is the FRW Metric and How Is It Applied in General Relativity?

    Homework Statement (a) Find the FRW metric, equations and density parameter. Express the density parameter in terms of a and H. (b) Express density parameter as a function of a where density dominates and find values of w. (c) If curvature is negligible, what values must w be to prevent a...
  37. Calpalned

    Green's Ellipse (Move to Math homework)

    Homework Statement Homework Equations N/A The Attempt at a Solution Question 1) Suppose I tried to convert ##\int \int_c {-2y^3} dA## into polar coordinates. What would the limits be? I know that ##x = rcos(\theta), y = rsin(\theta)## but the two rs are different (unlike in a circle). Q2)...
  38. U

    What Are the Steps to Solve Einstein Equations for This Metric?

    Homework Statement [/B] (a) Find the christoffel symbols (b) Find the einstein equations (c) Find A and B (d) Comment on this metric Homework Equations \Gamma_{\alpha\beta}^\mu \frac{1}{2} g^{\mu v} \left( \partial_\alpha g_{\beta v} + \partial_\beta g_{\alpha v} - \partial_\mu g_{\alpha...
  39. U

    What Are the Steps to Solve This Space-Time Metric Homework?

    Homework Statement (a) Find ##\dot \phi##. (b) Find the geodesic equation in ##r##. (c) Find functions g,f,h. (d) Comment on the significance of the results. Homework Equations The metric components are: ##g_{00} = -c^2## ##g_{11} = \frac{r^2 + \alpha^2 cos^2 \theta}{r^2 +\alpha^2}##...
  40. D

    Homework Help on Kirchoff's Laws and Magnetic Induction

    Homework Statement I am stuck on 2 and 3. I attached all the problems and variable and unknownsHomework Equations I attached my work for 1, 2, and 3. I'm not sure if it is right though. [/B]The Attempt at a Solution Can someone check my work for problems 1, 2, 3 and 4? The equations...
  41. goonking

    Solving Homework: Understanding Equations

    Homework Statement Homework EquationsThe Attempt at a Solution I chose the answer A, but it's not correct, can anyone explain why?
  42. R

    Need help with Newton's Law of Cooling math problem

    A detective finds a murder victim at 9 AM. The temperature of the body is measured at 90.3-degrees Fahrenheit. One hour later the temperature of the body is 89.0-degrees Fahrenheit. The temperature of the room has been maintained at a constant temperature of 68-degrees Fahrenheit. Estimate the...
  43. GiantSheeps

    Wavelength given time, velocity, and cycles

    Homework Statement As your hand moves back and forth to generate longitudinal pulses in a spiral spring, your hand completes 2.88 back-and-forth cycles every 6.98 s. The velocity of the pulse in the spring is 0.581 cm/s. What is the wavelength? Answer in units of m. Homework Equations v=λf...
  44. L

    The average density of halo of non-baryonic dark matter?

    I've got a homework question that I'm particularly stuck on: Suppose that the halo, assumed spherical, of non-baryonic dark matter surrounding our galaxy has mass ~ 5 x10^12 M solar and radius 0.1 Mpc. What it its average density in Kg m-3? I think that I need to use the formula...
  45. 1

    Why is there a vertical force on the pin in this static equilibrium setup?

    Q: Why does the pin have a vertical force in this diagram (Static equilibrium)? The diagram depicts as follows: A mass (M) sits a a distance (d) away from the end of a board of length L. The board has a mass of m and is held to a wall by a pin and string. The string has a tension (T) and is at...
  46. U

    Which particle decays more frequently in Pi+ decays: muon or electron?

    Homework Statement Draw feynman diagrams for pi+ muon lepton decay and suggest which process is more likely.Homework EquationsThe Attempt at a Solution [/B] The feynman diagrams are: The lepton decays proceed via the weak interaction W+ boson. This implies that e+ should be...
  47. papaross

    Finding properties of a linear transformation

    Homework Statement Find the domain, target space, image, rank and nullity of the linear transformation T(A)=Av, where v= (1, 2) and A is any 2×2matrix. Homework Equations The Attempt at a Solution I believe I know the domain (R2x2 vector space) and target space (R2), but I am not sure how to...
  48. C

    Work and isothermal compressibility

    Homework Statement 1 kg of water is at room temperature and the pressure is isothermally increased on the system from 1 atmosphere to 1000 atmospheres. What is the work done? What is the change in heat? What would be the temperature change if this was done adiabatically? The volumetric...
  49. GiantSheeps

    How Does Position Affect Gravitational Force Between Three Objects?

    Homework Statement PART 1: Objects with masses of 125 kg and 548 kg are separated by 0.385 m. A 63.5 kg mass is placed midway between them. Find the magnitude of the net gravitational force exerted by the two larger masses on the 63.5 kg mass. The value of the universal gravitational constant...
  50. 1

    Conservation of Angular Momentum & Energy question

    Question: A streetcar is freely coasting (no friction) around a large circular track. It is then switched to a small circular track. When coasting on the smaller circle its speed is: a) greater b) less c) unchanged Relevant Formulas: w = v/r KE = 1/2mv2 My teacher said the normal force from...
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