# Search results

1. ### Choosing between GW and CM modelling

Hello PF, I am in a bind and wonder if anyone has any advise. Finishing my undergraduate learning I applied for numerous PhD positions, and was incredibly lucky to receive the following offers 1) Modelling of complex systems specializing in magnetic materials (condensed matter...
2. ### A mass between two springs-simple harmonic motion

Hello cnputhur, welcome to PF. Your solution to the first question is the correct magnitude. However your minus signs may have gone awry. Try labeling the forces in future to help with these things ( a diagram will then make it very clear which way it must go). And for question 2?...
3. ### A boy sliding down an incline removes jacket how does this affect speed and momentum?

Mathematically I would argue it something like: The total energy of the system must be conserved, therefore \textrm{K.E} + \textrm{P.E}= \textrm{const.} \Rightarrow \frac{1}{2}mv(x)^{2} + mgh(x)= \textrm{const.} The constant is arbitrary since we can define the potential as we...
4. ### Harmonic motion problem

You have worded this question somewhat strangely but I will attempt a solution. Think of the particle under SHM as a Pendulum clock (or weight on the end of a string). If it is "ticking" then ask "what is the velocity" at these two points: 1) When it is at maximum displacement from the vertical...
5. ### Resolve forces along a pivot

Hi, when you say a force of 235Kg this does not make any sense. A Kg is a Mass, so under the acceleration of gravity it will have a force 235g=2350N in the negative vertical direction. Since your diagrams do not provide this direction I can't tell you if you are making a mistake...
6. ### Resolve forces along a pivot

Hello mathuria1986, This could be quite complex to solve, or simple depending on how this system is orientated with respect to the local gravity. The 300Kg mass will have a force F=ma along this local gravity. You have drawn it such that there is an angle 23' to the x axis (call it the x...
7. ### Proportion Problem Dealing with Moon's Period

I have no idea about a maximum number of votes, but who cares anyway! Proportions are okay if you think about them in a good way (as with most things). Personally I like to introduce a constant so the statement "T is directly proportional to (r)^3/2" I would write as T \propto r^{3/2}...
8. ### When you drive a .36 kg apple, Earth exerts a force on It that

Hello KellySierra22, Instead of giving your workings with numbers, it is easier to understand the problem in algebra. We start with the well known F=ma, however we must be careful about which force and which mass (although the acceleration is constant). So I...
9. ### Lorentz Law field equation applied in a field

Well done, that is fine remember to include the direction as well as the magnitude! All the best
10. ### Lorentz Law field equation applied in a field

You can calculate the electric field using Gauss's law. And E(r) = Q / 4πε r^2, I believe is from a single point charge. You will need to calculate it for a wire a good discussion is given hear http://farside.ph.utexas.edu/teaching/302l/lectures/node26.html
11. ### Lorentz Law field equation applied in a field

You may use that F=qVB when there is no electric field and the magnetic field is perpendicular to the direction of motion. To understand this consider that \overline{v} \times \overline{B}=|\overline{v}||\overline{B}| \sin( \theta) \hat{n} Since the magnetic field will be a loops in the...
12. ### Thermodynamics/Statistical Mechanics Probability Questions

I don't really think an understanding of equipartition theorem is required further than what Wikipedia can provide. Just consider it a big statistical problem (you have no interactions) and should be okay.
13. ### Component acceleration in free-body diagram

Indeed you have spotted your own mistake, when writing out the component of the 3N force along x, try to imagine two vectors parallel to the y and x axis. The magnitude of these is what you are physically trying to find. You have written that F_{x,2}=(−3)⋅\cos(110)≈1.03 I try not to...
14. ### Component acceleration in free-body diagram

Hello octowilli, Thank's for providing nice diagrams and explanations of your attempt, in particular well done for solving algebraically before finding a numerical answer. However you have become slightly unstuck when calculating the forces along x, I fear it may be a...
15. ### You throw several coins into a pool for a diving game

Hi nomalware80, have you tried these questions at all? Where do you get stuck, have you tried chucking some coins in a glass of water to answer questions 1.
16. ### Lorentz Law field equation applied in a field

It sounds like you are very close: The more straightforward F = qvB(r) is true when you don't have an electric field and the velocity is perpendicular to the magnetic field, however you must be careful in the direction as there are some minus signs in a cross product like that. Rather...
17. ### Determination of Earths radius with known latitude and sun travel times

Firstly find the radius of the earth of your latitude by considering the quantities you have. Personally I would approach this by using ratio's you know the length of a day, the time between you and your friend and finally the distance. Once you have this radius you need to assume the earth is...
18. ### Potential energy of a spring and transverse motion

Exactly, so now you can find the magnitude of the force easily enough, the rest follows from this.
19. ### Potential energy of a spring and transverse motion

You do not know that the work done is the same, you just follow the prescribed method to determine it. I'm getting a bit confused by what you mean by What do you think is the answer to question a), Ie L(x)=? once you know this, then you can consider the force needed to extend the spring by...
20. ### Potential energy of a spring and transverse motion

For a) you need to parameterise the amount it has stretched in fig b as a function of x. Geometrically think of take the stretched spring in b, and rotating it back to vertical. Then consider the relation between the extrat height L(x) and the distance it was moved x. After this I presume you...
21. ### Definition of Capacitance

I am inclined to answer although I am not 100% this solution is correct so please tell me if this is wrong. As I'm sure your aware we calculate the capacitance for two concentric circles by C=Q/V \; , where from Gauss's law we draw a sphere around the smallest shell. V=\int_{a}^{b}E dr =...
22. ### Exchange coupling constant in micromagnetic simulation

Hi, Not sure if you still require this information but I am doing some similar work, using Nmag. The manual for this tool contains some generic value's mostly for Permalloy (Nickel-Iron) which should be about 13e-12 J/m . If you do find a better source please let me know as I am...
23. ### Third resonance length frequency(which formula do i use?)

I am confused as to your adding lengths, this may just by my understanding though. If I were to do this question then I would draw a diagram, importantly the open ends mean both ends must have nodes. So the first mode as you mentioned will have no nodes inside the pipe, therefore the wavelength...
24. ### Formula help

What sort of mass? Without context usual mass density is simply the mass you have over the volume it occupies.
25. ### Thermal radiation experiments

Hi There, I will firstly say I am no expert in this field but your statement: It is my understanding that in a solid, the atoms are arrange in a lattice with tight bonds. Therefore when considering the three heat transfer mechanisms, conduction, convection and radiation...
26. ### Can anyone advise on the strength of modelling/theory groups in the UK

I am in the fourth year of an MPhys and feel a PhD is the best way to further myself. I want to apply to groups that specialize in the theory and implementation of computational modelling. I would prefer this to be a group with a wide range across several branches of Physics as opposed to a...
27. ### Physics Vectors

I am unsure what you mean by the range equation, but from it's form I would guess you mean r^2=x^2+y^2 , that is Pythag' which would be the square of the physical distance the rock lands away. You are asked for the "speed" which I am sure you are aware is a magnitude of the velocity (a vector)...
28. ### Physics Vectors

Firstly, the question should have states "how" the stone was launched. I will assume it was horizatontally thrown with the given speed. If this is the case, then you must split the problem into two orthogonal directions, the obvious choice being x,y (where y is vertical). Then you know the...
29. ### Shallow wave equations (First order quasilinear systems)

Homework Statement I am trying to show the shallow wave equations (Pg 35 Ockendon). For a shallow channel of water, with one free surface h(x,t) that runs parallel to the x-axis, the fluid has a constant density and the pressure is nearly hydrostatic and equal to P(x,t)=ρg(h-y) Homework...
30. ### Thermal/Energy Radiation

Firstly you need to realize what information the question has given you, namely that the sphere radiates 4.3 J/s^2. Recognize that this is a power (Power=Energy per unit time) and you have an expression which relates some variables with the Power it will emit. Since it does not give you...