Applies to questions of primarily educational value - not only questions that arise from actual homework assignments, but any question where it is preferable to guide the asker to the answer rather than giving it away outright.
0
votes
1answer
1k views
Finding Phase angle of Simple Harmonic Motion?
A sinusoidal oscillator has :
$$x=x_{max} \cos(\omega t - \varphi )$$
Period is 2, initial displacement is 100mm
initial velocity is 200mm/s
What is the phase angle assuming $-\pi < \varphi < ...
2
votes
1answer
684 views
Confused with stress, strain and linear thermal expansion
Four rods A, B, C, D of same length and material but of different
radii r, 2r , 3r and 4r respectively are held between two rigid
walls. The temperature of all rods is increased by same ...
0
votes
2answers
94 views
The time for which rear moving block remain in contact with spring in the following situation? [closed]
I'm a physics tutor. I'm stuck up with this question. I've no clue about how to proceed with this question. Can any one help?
A 2 Kg block moving with 10 m/s strikes a spring of constant π^2 N/m ...
0
votes
2answers
385 views
Help me find electric field strength vector for this given equipotential line
I'm a physics tutor. This is the question from a High school book.
The equation of an equipotential line in an electric field is y = 2x,
then the electric field strength vector at (1, 2) may be ...
0
votes
2answers
315 views
The energy of electric interaction between these dipoles?
I'm a physics tutor. This is not a homework problem. I'm unable to solve this problem.
The energy of electric interaction between these dipoles will be:
Choose the correct answer from:
I tried ...
1
vote
2answers
551 views
Calculating Impact Velocity Given Displacement and Acceleration
Assume a car has hit a wall in a right angled collision and the front bumper has been displaced 9 cm. The resulting impact is 25g. Also, it is evident by skid marks that the car braked for 5m with ...
2
votes
0answers
263 views
kinetic energy in collisions
We were hoping you could help us understand collision energy.
Vehicle A is driving West at 35mph and weighs 1437kg.
Vehicle B is driving North at 35 mph and weighs 1882kg.
Vehicle B crashes into the ...
1
vote
0answers
176 views
Is the $mL_c$ value for triangular and rectangular fins the same value?
I am looking at the solutions that my professor put up and I feel that he did something wrong. Here is the question and I will give my stab at the solution so you can see why I think that it is wrong.
...
1
vote
1answer
319 views
Work and Area under a Curve relating to Hooke's Law
If it takes work W to stretch a Hooke’s-law spring (F = kx) a distance d from its unstressed length, determine the extra work required to stretch it an additional distance d (Hint: draw a graph and ...
0
votes
1answer
142 views
M1 vs M2 on a frictionless surface
I was wondering, if I had a frictionless surface and I had an M1 that was 100kg and an M2 that was 1kg and I pushed each separately with an equal force F would they move at the same speed or am I ...
-1
votes
1answer
201 views
resonance frequency [closed]
A string has a mass per unit length of 9 10–3 kg/m. What must be the tension in the string if its second harmonic has the same frequency as the second resonance mode of a 2m long pipe open at one end? ...
1
vote
4answers
669 views
17 Joules of Energy From a Mouse Trap
Do you think it would be possible to get 17 joules out of a standard size mouse trap. By my math, it is a torsion coefficient of 3.45 or so out of the spring.
1
vote
2answers
1k views
Finding distance when the force is a function of time
I'm having trouble with this homework question
A mysterious rocket-propelled object of mass 49.0 kg is initially at rest in the middle of the horizontal, frictionless surface of an ice-covered ...
1
vote
1answer
136 views
Finding the contact force in a mechanical problem [closed]
what is the proper FBD for this system. I cant decide since the weight is given, but there is tension and contact forces. Things get mixed up.
Determine the contact force between the smooth 200-lb ...
2
votes
1answer
279 views
How do I find average temperature given a temperature distribution?
I was told to find the temperature distribution of a wire with a current going through it. So I found $$T(x)=T_{\infty}-\frac{\dot{q}}{km^{2}}[\frac{cosh(mx)}{cosh(mL)}-1]$$
I need to find the ...
2
votes
1answer
439 views
How is capacitance defined for three concentric spheres?
If we have a configuration of metal concentric spheres (each of negligible thickness) of radii $r_1,r_2,r_3$ respectively and $r_1<r_2<r_3$, and we are given the potentials of the spheres to be ...
1
vote
1answer
384 views
Why is it wrong when I try to use Newton's Law?
A 25 kg block is connected to a 30 kg block by a light string that passes over a frictionless pulley. The 30 kg block is connected to a light spring of force constant 195 N/m, as in Figure P13.59. ...
0
votes
1answer
55 views
Potential at a point
What is the electric dipole moment of the charge distribution with $q$ at $(0,0,1)$, $q$ at $(0,0,-1)$ and $-2q$ at $(0,0,0)$? I would think that it is $\vec{0}$ by the definition ...
1
vote
1answer
245 views
Solving Schrödinger's equation for a specific potential
I am trying to solve this differential equation:
$$-\chi''(\epsilon)+\Big[\epsilon^2+\frac{2F}{hw}\sqrt{\frac{h}{hw}}\epsilon \Big]\chi(\epsilon)=\mu\chi(\epsilon) \tag1$$
This was found ...
-1
votes
2answers
142 views
Show that the energy levels of a particle in a specific potential are $E_n=(n+\frac{1}{2})h\omega-\frac{1}{2}\frac{F^2}{m\omega^2}$ [closed]
A particle of mass m moves on the x-axis under the influence of the potential
$$V(x)=\frac{1}{2}m\omega^2x^2+Fx$$
Can anyone help me, using Schrödinger's equation in one dimension that the energy ...
3
votes
1answer
348 views
Given charge distribution find electric field
Given a charge distribution $\rho(\vec{r})$ where $\vec{r}$ is the position vector and that $\rho$ is a function of only $|x|$, Why is it that the corresponding electric field $E$ is necessarily of ...
0
votes
0answers
321 views
Evaluating Transition probability between different states of Hydrogen atom
I am trying to evaluate the inner product $<2S_{\frac{1}{2}},F',F'_{3}|\delta^{3}(x)\sigma_{i}P_{i}|2P_{\frac{1}{2}},F,F_{3}>$ It's written in the form $<nl_{j},F,F_{3}|$ Where ...
0
votes
1answer
189 views
Laws of Motion: Acceleration to be applied on a free falling object to reduce velocity to 0
Assume that an object of mass 'm' is falling to the earth.The force acting on the same would be F = m*g = 10m (assuming g = 10m/s^2). In this case the velocity of the object at time 't' = 10 seconds ...
1
vote
2answers
75 views
Acceleration: Value Disparity?
If we consider a ball moving at an acceleration of $5ms^{-2}$, over a time of 4 seconds, the distance covered by the ball in the first second is $5m$. In the 2nd second will $5 + 5 = 10m$. In the ...
1
vote
1answer
283 views
Calculating the force of a mass bearing down on an object
I need to calculate the force of a weight bearing down on a smaller object, constraining it from expansion.
The weight bearing down has a much bigger surface area than the smaller object.
I know the ...
3
votes
1answer
350 views
How to calculate the Gibbs free energy out of a given Entropy?
I'm stuck in a small calculation. I try to solve a small exercise.
You should calculate for a given entropy the Gibbs free energy, where the entropy is given as
$S\left(U,V\right) = ...
1
vote
1answer
3k views
How to find maximum velocity
I stack a question about projectile question.
The question was
A projectile is being launched from ground level with no air resistance. You want to avoid having it enter a temperature inversion ...
0
votes
1answer
295 views
Force and Laws of Motion [closed]
While catching a fast moving cricket ball, why do fielders gradually pull back their hands backwards with the moving ball? Please advice which among the following is the correct answer. If both are ...
-1
votes
1answer
320 views
How to get angular acceleration from spin count and angular velocity [closed]
It would be very good if someone explained me how do you get to the final answer which is already know (3.2 rad/s^2)
Have been given:
ω = 20 = angular velocity (rad/s)
N = 10 full spins
Need to find:
...
0
votes
0answers
64 views
Relativity Scenario [closed]
Does anyone have any ideas about this scenario? I'm having trouble comparing what happens at the different speeds. It has to do with simultaneity
Suppose Al is at rest standing in between two sets ...
-1
votes
2answers
1k views
How to find minimum velocity without time? [closed]
I have a physics problem that says
A 76.0-kg boulder is rolling horizontally at the top of a vertical cliff that is 20m above the surface of a lake. The top of the vertical face of a dam is ...
0
votes
2answers
350 views
How to compute drag coefficient given initial position, initial velocity and final resting position?
The equations I'm using are:
x = x + (DT * vx)
vx = vx * C
My DT is always 0.01 and the coefficient C (related to a linear ...
2
votes
4answers
889 views
Divergence of $\frac{\vec{r}}{r^2}$
In David J. Griffiths 'Introduction to ELECTRODYNAMICS' , as one the excercize he gave the following problem.
Sketch the vector function: $$
\vec{v} = \frac{\vec{r}}{r^2}
...
0
votes
1answer
885 views
As ISA Practical - Resistors in Parallel [duplicate]
Possible Duplicate:
Current against the inverse of resistance graph, I = V/R +c
How would you set up a circuit with a fixed resistor in parallel with a variable one. We are told to measure ...
2
votes
1answer
99 views
Pushing, inertia of a cart system
I have a cart with another cart on top which gets pulled down by another cart on the side. There is no friction.
The question is:
How strongly do I have to push with $F$ to keep the cart $m_1$ ...
0
votes
1answer
82 views
How to calculate the potential of the ball? [closed]
Consider 2 metals ,the smaller sphere has a radius of a carry +Q charges,what is the potential at the surface of the smaller sphere?
0
votes
1answer
183 views
Angular velocity $\omega$ by $v$
We have two girls, with mass (M). They become close to each other in speed of V. The distance between them is 3L.
I was asked to calclute the Angular velocity (w) of the two girls. So I set the ...
0
votes
1answer
320 views
Vibrational motion of linear diatomic molecule
This question concerns the following exercise from an old exam:
The vibrational motion of a linear diatomic molecule can be approximated as simple harmonic motion.
A CO molecule has a bond ...
1
vote
0answers
173 views
Exam review question on thermodynamics [closed]
A cube has a side length of $20\text{ cm}$.
An atom in the gas moves around the cube as shown.
It continually bounces off the four lateral walls of the cube.
The atom has a mass of $6.6\times ...
1
vote
1answer
257 views
Finding coefficients of volumetric expandtion from a know coefficient of linear expandtion
Starting from a homework problem:
An aluminum cup of $100 cm^3$ capacity is completely filled with glycerin at $22°C$. How much glycerin, if any, will spill out of the cup if the temperature ...
-1
votes
1answer
113 views
Force on pneumatic cylinder [closed]
A pneumatic cylinder is kept vertically straight on a weighing scale, which is set at 0 for the setup.
now a force of 1000 N is applied on the cylinder.
what is the reading of scale.
assume the ...
0
votes
1answer
193 views
When to use Heat Diffusivity eqn and when to use Fourier's law to find temperature distribution?
Let's say that there is a circular conical section that has diameter $D=.25x$ without any heat generation and I need to find the temperature distribution.
Originially I thought I could use the heat ...
1
vote
1answer
773 views
change of resistance in semiconductors due to temperature change
I have a question that popped up in an old exam I just can't find a way to solve.
If you drop the temperature of this material from room temperature (I guess around 300K) to 0C (273K) the ...
0
votes
0answers
113 views
Dynamo-meter and forces problem [closed]
I have this system:
Where D stands for dynamo-meter, and you can exclude all lines\dynamo-meters\balls weight and friction.
The left ball connects to body A, and the right ball connets to the wall.
...
0
votes
2answers
187 views
Problem based on Rotational Motion #2
One fourth length of a Uniform Rod of mass $m$ and length $x$ is placed on rough horizontal surface and it is held stationary by means of a light thread as shown in the figure. The thread is brunt ...
-1
votes
1answer
258 views
Minimal kinetic energy during elastic collision [closed]
Two wagons, moving towards each other along a straight line, collide. The first wagon has the speed 3 m/s and the weight 3 kg. The second wagon has the speed 1 m/s and the weight 1 kg. The collision ...
0
votes
1answer
229 views
Finding The Resultant Vector [closed]
A plane is flying southeast at 215 km/h. Suddenly there is a wind from the north at 75 km/h. What is the plane's new velocity with respect to the ground in standard position?
0
votes
1answer
130 views
Expansion of Helmholtz energy
To get an expansion of Helmholtz energy of
a) an ideal gas
b) a Van der waals gas
we must integrate
$\left ( \frac{\delta A }{\delta V} \right )_{T}=-P$
I saw the solution is :
Can you ...
1
vote
3answers
409 views
One dimensional Schrödinger equation equation with initial condition, finding the probability of the particle's future position
A particle of mass $m$ moves freely in the interval $[0,a]$ on the $x$ axis. Initially the wave function is:
$$f(x)=\frac{1}{\sqrt{3}}\operatorname{sin}\Big( \frac{\pi x}{a} ...
0
votes
2answers
1k views
Find the Unit Vector of a Three Dimensional Vector
How can I find the unit vector of a three dimensional vector? For example, I have a problem that I am working on that tells me that I have a vector $\hat{r}$ that is a unit vector, and I am told to ...
