# Homework help Definition and 342 Discussions

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. ### Work calculation for lifting a Tetrahedron-shaped object from the water

Hi, I'm calculating the work done by regular tetrahedron during taking from the water by crane (USING INTEGRALS). I don't know how bad is that solved so if anyone checks my work and gives me some advice or hints I would be very glad. Everything is written in the PDF file. There were given...
2. ### Engineering Using Virtual Cantilevers to Derive Bending Moment for Indeterminate I-Frame

Diagram of the problem below. I have 45 minutes to finish all parts of this question without reference material. The Mechanics of Materials section of these tests are largely Structural Analysis, which I was not taught to this level in my undergrad degree so I am teaching myself via Youtube...
3. ### Engineering Fluid mechanics question and the Bernoulli Equation

Good afternoon, I am struggling to find the solution at Q2 and Q3. For Q2 the absolute pressure at point 1 is at the bottom of the tank, so do i need to use the formula P=Patm+qgh ? If using this formula I've got a bigger number than 100Pa. Same issue for Q3, isn't the pressure at point 2...
4. ### The lowest possible plane altitude for a dropped projectile to hit the target in a hole

A plane is flying 80km/h in horizontal direction and it has to drop a bomb into 30m wide and 30m deep hollow. What is the smallest possible height for the plane to fly above hollow if the bomb successfully hits the bottom? I made a mistake somewhere but not sure where... the correct result is...

6. ### I don't understand this problem -- Surface area of a section of a solid sphere

Sorry i don't understand English very well , if someone want to explain to me this problem?
7. ### Time of flight for a ball thrown straight upward versus thrown upward at an angle

Vertical components: dy = 0m ay = 9.8m/s^2 [down] t = 1.34s V1y = required V2y = 0 i first tried to find V1y dy =vi t + 1/2 a t^2 and got V1y = -6.566 then i solved for time of flight dy =vi t + 1/2 a t^2 0 = -6.566t + 4/9t^2 and for 1.34 seconds does this mean the time of flight is the...
8. ### Chemistry Bronsted-Lowery help needed

1) HCOOH + CN- ---> HCOOH- + HCN 2) H2O + HCO3- <===> H3O+ + CO3-2
9. ### Thermal physics question: Specific heat capacity

At first, I tried to calculate the heat energy required by doing this: I realized I should calculate heat energy separately instead of grouping glass and water together so I did this: But the answer is supposed to be 6.29 x 10^4. I don't know how to solve this. Can anyone help please? Thank you
10. ### How to calculate error on log(MW) and error on MW for an SDS-PAGE calculation?

I have found my LINEST equation for my standard curve, which is where y=log(MW) AND x= Rf y=-1.392047709x+2.324113743 as well, my imageLab gives me: Relative Front (Rf) = 0.087 error on Rf=0.005 I can calculate my log(MW) by inputing my Rf into x value of the equation...
11. ### Motion of a particle

This is jut an example to illustrate my doubt. I don't know how to obtain the tracjectory given only the acceleration in this format. I realized that if i can show that there is an constat vector 'a' that satisfy a•r=constant, than the motion would be on the surface of a cone. So i tried to make...
12. ### Comp Sci Harmonic Amplitudes - 3rd & 101st

I have attempted the question using the large formula here with figures from the waveform with n as 3 & 101: however I think that the large formula is for the total waveform encompassing all harmonics as the 3rd and 101st harmonic amplitudes are very similar 10.9662222 *10^-6V for the 3rd...
13. ### Falling Chain (David Morin)

Firstly, There is something I want to clarify. When the system starts moving, parts of the chain that still lies on the table, which have mass ## \frac {(L- y_0)M} {L}##, will be pulled by the force that the hanging chain's weight exert,right? If yes, then : As far as I know, the formula ##F=...
14. ### Work & Energy (Question on Classical Mechanics/Slope based Problems)

I used the Change in Kinetic Energy and equated that with the Work Done. The "Work Done" part comprises of two different functions- one is work done by Gravitational Force while the other is the work done by frictional force (or the brakes). /Delta KE (magnitude wise)= 0.5*1350* (20^2)=270,000...
15. ### Maxwell's Distribution Law (Thermal Physics)

There are two questions in the photo. I have attempted the solution (attached below) and I would be highly obliged if someone would verify the same. Edit- Sorry the images of the solution have uploaded in the wrong order. 5th and 1st Image comprise of both parts of Q1 while the remaining of Q2.
16. ### Question on First Law of Thermodynamics (Paramagnet)

For the first part, I have expressed it in the following differential form- dU= delta (Q) + BdM Now for the second part I am having major confusion. I know that B corresponds to P and M corresponds to V as generalised force and generalised displacement respectively for a Paramagnetic substance...
17. ### A mass collides with an inclined plane

In my textbook, it is stated that "if an object elastically hit an frictionless inclined surface with angle between the vector of initial velocity and an imaginary line that is perpendicular to the surface ##\alpha##,then the angle between the line and final velocity vector will also be...
18. ### Engineering Complex Thevenin's Circuit

So I've been absolutely stumped on this one. I've tried about a million different things but none of them have seemed right. A combination of the odd layout of the circuit, and a combined voltage/current source are making things really complicated for me. I'm somewhat sure the RTh is 15kΩ due to...
19. ### Question on how much intensity of light has been scattered

I actually am not sure what equations are relevant here but I thought these are the relevant ones. My Approach: By Stefan-Boltzman Law, the intensity absorbed by the Earth is given as ## I = e \sigma T^4## where e is the emissivity of Earth, ##\sigma## is Stefan-Boltzman constant and T is the...
20. ### Some homework questions in astrophysics (Kepler's Laws, Newton's Laws)

1. Keplers third law (and the asumption that M1+M2 ~ M1) gives that M_Mars = 4*Pi^2*a^3/(G*T^2) With numerical values inserted Mmars = 4*3.14^2*(9400*1000+3396.97*1000)^3/((6.67*10^-11*(7*60*60+39*60)^2) 2. Phobos needs 7h39 minutes to complete a circle, this gives a speed of...
21. ### Why a 20 Ohm lightbulb won't light up in a closed circuit?

When using the voltmeter and ammeter to investigate the circuit, it was found that the batter had a current of 0.67 A, the two 30 Ω bulbs had a current of 0.17 A, and the two 10 Ω bulbs had a current of 0.50 A. In terms of voltage, each bulb had a voltage of 5 V. When the switch was closed, the...
22. ### Applications of Newton's laws - coefficient of friction

https://www.physicsforums.com/attachments/277763
23. ### Fluid dynamics calculation -- Draining a barrel through a pipe

v1- velocity of water at the top of the barrel v2- velocity of water at the the pipe (bottom of cylinder) p + (⍴ *(v1)^2)/2 + ⍴gh=p + (⍴ *(v2)^2)/2 + ⍴gh atmosferic pressure cancels out (⍴ *(v1)^2)/2 + ⍴gh = (⍴ *(v2)^2)/2 + ⍴gh density doesn't affect the result(cause its in every term)...
24. ### Help please solving this electromagnetism problem -- coil moving near a magnet

A small coil is moved forward (without turning) between the poles of the electromagnet. Does an electric current develop in the coil? Explain the answer
25. ### First time Pre-Calc student, HW Help with Goose

150 km tan(35)=150/x Hyp=316.58 I know this isn't right where did I go wrong or did I even start correctly
26. ### Determine the force in the bar CB

I solved this with two methods as you can see down below in the picture. Which is the correct way? I remember I learned in class you could use both ways but why am I getting different results?
27. ### Refraction in a swimming pool

The first sketch is what I assumed would happen, where the light beams bends. And the second is meant to depict the light forming a cone, which I don't understand. [Mentors provided help re-posting the image that was missing]
28. ### Physics Homework Question on terminal velocity and weight

Below I've attached the question - I don't know why this question is so difficult, perhaps I missed a lesson or such, however I've Benn working at it for ages and got nowhere...
29. ### Finding the generator of rotations for a 3-state triangle

I first computed the operator ##\hat{T}## in the ##a,b,c## basis (assuming ##a = (1 \ 0 \ 0 )^{T} , b = (0 \ 1 \ 0)^{T}## and ##c = (0 \ 0 \ 1)^{T}##) and found $$\hat{T} = \begin{pmatrix} 0&0&1 \\ 1&0&0 \\ 0&1&0 \end{pmatrix}.$$ The eigenvalues and eigenvectors corresponding to this matrix...
30. ### A strange wave function of the Hydrogen atom

I am trying to solve the following exercise. In a H atom the electron is in the state described by the wave function in spherical coordinates: \psi (r, \theta, \phi) = e^{i \phi}e^{-(r/a)^2(1- \mu\ cos^2\ \theta)} With a and \mu positive real parameters. Tell what are the possible values...
31. ### Sending a sound wave of 1cm wavelength through a 0.1Pascal medium

I answered the first part of the question where I estimate the radius of ##O_{2}## is ##\approx 1.5 \times 10^{-10} \ \text{m}##: $$p = \frac{KT}{l 4 \pi r^{2}} = \frac{(20+273.15)(1.38\times 10^{-23})}{(0.1)(4\pi)(1.5 \times 10^{-10})^{2}} = 0.143 \ \text{Pa}.$$ The confusion arises on the...
32. ### Verifying that the uncertainty is 0 for a QM state

By definition , ##\ket{+x} = \alpha \ket{+z} + \beta \ket{-z}.## Therefore we proceed , \begin{align*} \langle S_{x} \rangle &= \lvert \alpha \rvert^{2} \left(\frac{\hbar}{2}\right) + \lvert \beta\rvert^{2} \left(-\frac{\hbar}{2}\right) = (\alpha^{2} - \beta^{2})\left(\frac{\hbar}{2}\right).\\...
33. ### What is the resulting force between the beam CB and E?

I assumed that the vertical force at point B would be the same as the force between beam CB and E because of Newtons law. Did I assume wrong? Look below for my calculations and answer which I got to 250N. I don’t know the correct answer but assume someone here can tell me if I solved the problem...
34. ### Interpreting a thermodynamics formula using a picture

I notice that ##pv=t## looks like the ideal gas law but with ##T## in units of energy. I know that ##pV = \text{constant}## means that the pressure of a gas decreases as you expand it (Boyle-Mariotte's law), explaining for instance how we breathe. I guess I could put everything in words even...
35. ### Density of water

Homework Statement:: The relative density of water is determined by the rate at which it expands (and contracts) with changes in temperature. At approximately what other temperature T does water have the same density as at 1 ∘C ? Relevant Equations:: Just looking at graphical and analyzing...
36. ### Divergence of a radial field ##F=\hat{r}/r^{2+\varepsilon}##

Following (1), \begin{align*} \text{div} F = \vec{\nabla} \cdot \vec{F} &= \frac{1}{r^2} \frac{\partial}{\partial r} \left( r^2 F_{r}\right) \\ &= \frac{1}{r^2} \frac{\partial }{\partial r} \left( r^2 \frac{1}{r^{2+\varepsilon}}\right) \\ &= \frac{1}{r^2} \frac{\partial}{\partial r}...
37. ### Comp Sci TextAnalyzer java code

My current attemp is: import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.IOException; public class TextAnalyzer { private int lineCount; private int wordCount; private int[] frequencies = new int[26]; public int...
38. ### Does the tension in a string act on the body to which the pulley is attached?

The normal reaction from the ground and from block m, the force of gravity are the forces I feel should act on the wedge but since the wedge is a perfectly rigid body and the pulley(which is massless) is attached to it so will tension also act on the wedge as well?
39. ### Two blocks kept side by side and friction between them

if the applied force F >(M+m)g/##\mu## the force of friction between the two blocks should become f=N##\mu## and since the normal reaction will be greater than what it should be to keep the block m at rest with respect to M, will the mass m accelerate upwards. in short,for let's say a very...
40. ### Two block friction problem

when a force of 10N is applied to the 4kg block the force of friction between the two blocks will also equal 10N as the maximum value of friction between the two surfaces is f = N##\mu## = 20N. if you look at this free body diagram f = F = 10N so the net force acting on the top(4kg) block will...
41. ### Two pulleys lifting a mass in parallel

if the ends P and Q are being pulled down with a uniform speed its acceleration is zero and hence the Tension in the string will also be zero and if this is the case which force will make the block of mass M rise? is this a fatal flaw in the question?
42. ### Block on a wedge connected to pulleys

if the tiny block moves downward by an amount x, the wedge should also move forward by the same amount x as they are connected by the same string whose length has to remain constant, (by differentiating it wrt time we get speed) hence I concluded that v1 = v2, but my book says otherwise what is...
43. ### Calculating gravitational potential due to a uniform ring tilted at an angle

I tried finding the potential due to a small element dM of the ring let's say dV, the summation of dV for all the dM's of the ring will give the potential at the point P, but since every element dM of the ring is at a different distance from the point P I am unable to come up with a differential...
44. ### Tension in a whirling rope

the point on the string at a distance r from the pivot is rotating in a circle of radius r and hence a centrifugal force of magnitude mw^2r can be said to act on it where m = (M/L)r . hence the T = centrifugal force T = (M/L)(wr)^2 but my book says otherwise. also can the string with mass be...
45. ### Variable friction on an inclined plane and maximum velocity

This problem was from the chapter on Work and Energy so, I thought of using the principle of conservation of mechanical energy. Clearly, the potential energy of the block decreases by mgh (assuming the block has mass m). This energy should have been converted to kinetic energy, but it clearly...
46. ### Cauchy-Riemann Theorem Example in Physics

I was thinking of the wavefunction in QM but I'm not sure how it's used and when.
47. ### Engineering [University Hydrology]-Creating a storm hydrograph from a 60 minute UH

Hi guys, not sure if anyone can help me but I'm having a bit of an issue with creating a storm hydrograph from a 60 min unit hydrograph that is in 5 minute intervals. I've lagged the unit hydrograph by 60 minutes each net rainfall block while multiplying the respective net rainfall to the...
48. ### Is this solution correct? (amount of fuel needed for orbital maneuvers)

The kinetic energy of a ##m_s##= 1.5 kg satellite in an orbit of ##h## = 200 km = 200##\times 10^3## m is \begin{eqnarray*} K.E. &=& G \frac{m_s . m_e}{2(R_e+h)}\\ &=& (6.67 \times 10^{-11} \ \mathrm{N.m^2.kg^{-2}}) \times \frac{(1.5\ \mathrm{kg})\times (5.972\times 10^{24}\...
49. ### Energy for an electron in an accelerator

I honestly just have no idea where to start on parts c and b. I tried 1.1*10^-12 N x 3218 m for part a, which was right. But I'm lost on b and c. I'm also wondering if we have to include a gamma factor in any of this, but I'm unsure how or where. Any help would be amazing.
50. ### The amount of energy required to move a mass m from the center of the Earth to the surface

a) In the rough approximation that the density of the Earth is uniform throughout its interior, the gravitational field strength (force per unit mass) inside the Earth at a distance r from the center is gr/R, where R is the radius of the Earth. (In actual fact, the outer layers of rock have...