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Questions tagged [homework-and-exercises]

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. Please READ THE GUIDANCE IN META before asking homework-like questions.

3
votes
2answers
8k views

How to determine viscous damping coefficient of spring?

I'm trying to determine the viscous damping coefficient of a spring $c$. Read about it on Wikipedia here. The two equations which I have are: $f=-cv$ and $ma+cv = -kx$ I know the spring constant $k=...
0
votes
1answer
473 views

Electric field of a charged spherical surface [closed]

Figure The dielectric shaped as on the figure has dielectric constant $\varepsilon=\varepsilon\left(r\right)$ and free charge density $\rho=\rho\left(r\right)$. What is the electric field and ...
1
vote
3answers
27k views

Determine Charge With Electroscope?

You have three separate glass rods, and you know one is positive, one is negative and one is neutral. You also have an electroscope that is positively charged. How can you determine which rod is ...
0
votes
1answer
10k views

What affects the damping of a spring?

What variables affect the damping of a spring executing simple harmonic motion? What are the independent variables, and what variables would need to be controlled in an experiment? I'm attempting to ...
4
votes
2answers
736 views

If you are told an image is real and you know it was made by a single optic (either a lens or a mirror), which of the following must be true? [closed]

If you are told an image is real and you know it was made by a single optic (either a lens or a mirror), which of the following must be true? The image distance is positive. The image distance is ...
6
votes
1answer
32k views

How is formula for converting pressure from mmHg to Pa derived?

Today my younger brother asked me from where does the 1 Pa = 0.00750061683 mmHg formula for mercury barometer come. He needs a way to derive it, or an academic source which can be cited. After ...
-1
votes
1answer
447 views

projectile power with air resistance [closed]

I need to get the x/y values of a fired projectile given the angle of the initial power, and air resistance. The formulas I have are $$V_x=V_o \cos\theta$$ $$X=V_o \cos \theta t$$ $$V_y=V_o \sin \...
2
votes
3answers
2k views

Unit conversion help (school) [closed]

Can someone please help me explaining how to convert units in problems like the one below? I've done many things, but I am very unsure of all my methods. Could you tell me what steps should I take? $$...
4
votes
1answer
987 views

Plotting a SHO in matlab [closed]

I have no prior experience of using matlab. My teacher want me to solve this question. I have been trying for a couple of hours now with no luck, please help! The mass of 100 g hanging in a spring ...
1
vote
1answer
3k views

What makes zinc reactive?

What makes zinc so desperate to give up its electrons? Silver has one extra electron, and zinc has two, but why is zinc more reactive?
2
votes
2answers
2k views

Electric field at a point from a square surface

I'm trying to determine the electric field at a point P (located on the +Z axis) due to a square of side length [L] and centered at the x-y plane origin. The square has a constant surface density [s]. ...
1
vote
1answer
802 views

Mass fixed to a wheel - mechanics problem [closed]

I am struggling with a problem from classical mechanics. Imagine a massless wheel (to make it simpler) with a mass $m$ fixed to it rolling without slipping on a horizontal ground. If we now try to ...
1
vote
2answers
523 views

Finding $\psi(x)$ from Fourier modes [closed]

In quantum physics we've defined: $$ \psi (x) = \sqrt{ \dfrac{1}{2 \pi \hbar} } \int^{ \infty }_{-\infty } \phi (p) \exp \left( i \dfrac{px}{ \hbar} \right) dp $$ Now, $$a(k) \equiv \sqrt{ \hbar } \...
0
votes
1answer
1k views

Proving Operator identities (Quantum Physics)

How would I go about showing: $$\hat{A}^{\dagger} + \hat{B}^{\dagger} = \left( \hat{A} + \hat{B} \right) ^{\dagger}$$ for a pair of bounded operators defined everywhere on a Hilbert space?
6
votes
7answers
5k views

What properties do you need for building a tower?

When I was a boy I used to daydream about building a tower so tall that the top of it would project into near space. There would perhaps be a zero gravity area in the penthouse where my friends and I ...
2
votes
2answers
940 views

Forces on a simple flat slope [closed]

This diagram is of a block (b) moving down a ramp unaided. Taking gravity (g) as $9.8ms^{-2}$, and the mass of the block (b) as $0.2kg$, how can I find the force acting along the slope (f). BTW: the ...
1
vote
2answers
291 views

What is the possible potential?

The professor asked us to do this one: "..Determine all potentials $V(r,\theta, \phi)$ for which it is possible for find solutions of the time independent Schrodinger equation which are also ...
3
votes
1answer
5k views

How to solve this Schrödinger equation?

I am taking an intro level quantum mechanics class. Our textbook gives a problem like this: The deuteron is a nucleus of "heavy hydrogen" consisting of one proton and one neutron. As a simple model ...
3
votes
1answer
887 views

Hydrostatic equilibrium of a star - simplification math error

I am trying to do this question and getting stuck at interpreting what the question is asking for. $$dP/dR = -g(R)\rho(R) = -[GM(<R)/R^2]\rho(R).$$ Thus when we descend a distance $\Delta R$ ...
-1
votes
1answer
4k views

How does mass relate to resistance (Ohm's Law)

How can I relate $mg$ to $R$? Just to give you a scenario: If a free hanging weight was tied to a motor... I know the voltage ($V$) and current ($I$) so I can use $V = IR$ to find $R$. What if I ...
-1
votes
1answer
2k views

Finding the mass of bed/Patient [closed]

One of my friends has a problem and we don't know how to get this done, We want to to know the mass of a patient who is laying on a bed. One scales was put under the foot of a bed and weighed 232kg ...
4
votes
1answer
995 views

Electric Potential

A nonuniform linear charge distribution given by $\lambda = bx$, where $b$ is a constant, is located along an $x$ axis from $x = 0$ to $x = L$. What is the electric potential at a point on the $y$ ...
6
votes
1answer
14k views

How far will water squirt out from a hole in a can?

Say you have a bottle of water filled up to a height $H$. A small hole is drilled in its side at a height $d$, so that water squirts out. The squirting water travels in an arc as it falls, covering ...
1
vote
2answers
5k views

Projectile motion without air resistance [closed]

Does the mass of projectile affect its trajectory when it is projected in no air resistance environment and why?
4
votes
1answer
160 views

Identifying unrealistic traits of this exoplanet. There are a few obvious ones, but I can't find them all. Help! [closed]

I need to find the inaccuracies of this computer generated picture, the picture shows a non existent exoplanet. I need to identify the unrealistic features of the planet and its surroundings and write ...
4
votes
1answer
399 views

Kinematics textbook illustration

I have trouble interpreting this illustration. I see why r (position) and a (acceleration) are the way they are, but what happened to v? Why is it smaller than its coordinates? Is this another error ...
1
vote
1answer
322 views

Simple kinematics excercise, throwing something upwards [closed]

I am trying to solve this simple excercise: Question You throw a small coin upwards with $4 \frac{m}{s}$ . How much time does it need to reach the height of $0.5 m$ ? Why do we get two results? ...
0
votes
1answer
201 views

Standing Wave: How to show that $\frac{\mathrm df}{f}=0.5\frac{\mathrm dF}{F}$ where $f$ is frequency and $F$ is tension of the string?

How to do this? Show that if the tension $F$ in a string is changed by a small amount $\mathrm dF$, the fractional change in frequency of a standing wave, $\frac{\mathrm df}{f}$ is given by: $$\frac{...
2
votes
2answers
766 views

Calculating the deflection of an arbitrary beam of light from a thin lens

Suppose we have a lens with known focal length and are using the thin lens approximation. Is it possible to determine how an arbitrary beam of light will be deflected by it? Or, is it the case that ...
3
votes
1answer
2k views

Measuring the spring constant in a system with hydrostatic buoyancy

I have a physics lab tomorrow and I would appreciate it if you could give me your opinion on whether my reasoning is correct for this situation or not: http://i.stack.imgur.com/WMzA7.jpg The title ...
12
votes
9answers
40k views

What's the core difference between the electric and magnetic forces?

I require only a simple answer. One sentence is enough... (It's for high school physics)
0
votes
1answer
1k views

converting force from spherical to Cartesian coords

So I am working on my assignment, and have a question about converting coordinates. I dont know whether I should ask here or the math SE, so lets give it a try here. The force in question is $$\vec{...
0
votes
1answer
358 views

Angular momentum

I'm given with the following problem - it's an easy one, but it's nearly 1AM, I'm tired and I need some push into the general direction to get the solution: A particle is assumed to be in the state $...
4
votes
3answers
6k views

Symmetric potential and the commutator of parity and Hamiltonian

In one dimension - How can one prove that the Hamiltonian and the parity operator commute in the case where the potential is symmetric (an even function)? i.e. that $[H, P] = 0$ for $V(x)=V(-x)$
9
votes
4answers
23k views

Weight on carpet vs. hard floor

Will the scale say I weigh more, less, or the same on a carpet as compared to a hard floor? You can assume the scale works via spring mechanism. Free body diagrams encouraged!
3
votes
1answer
1k views

Ski Jumper's vertical velocity after $246.5m$ record?

What would be the vertical velocity of this ski jumper (ski flyer), after he first touches down, after he breaks the record with a $246.5m$ jump? What g force would he experience as he slows down? ...
0
votes
3answers
4k views

Impulse - distance question [closed]

What impulse should be applied to an object of mass m, having a known coefficient of friction u to get to a distance d ? Thanks! Update 14.02.2011: I still wasn't able to find an answer to this. ...
1
vote
1answer
6k views

Finding the steady state solution of a damped oscillator

A damped harmonic oscillator with $m = 10$kg, $k = 250$N/m, and $c = 60$kg/s is subject to a driving force given by $F_0\cos(\omega t)$, where $F_0 = 48$N. (a) What value of $\...
2
votes
2answers
3k views

Electric potential in a capacitor

Im a writing a school report regarding the electric energy and potential of a capacitor. In short: An experiment was carried out where we charged a capacitor, and then decharged it with an electric ...
1
vote
2answers
4k views

How long does it take a block to slide up and down a plane with friction? [closed]

So I am studying for my exam on monday for analytical mechanics. I am kind of stuck on a question, so wondering if someone can give me a pointer. I am actually looking for some pointers and some ...
1
vote
3answers
1k views

Understanding weight on an inclined plane

I'm trying to solve a problem where I have an object resting on an inclined plane, with the angle of the plan being alpha, and the weight being w. I'm having trouble figuring out how I can calculate ...
-1
votes
3answers
10k views

Vector product in 2 dimensions [closed]

If I have a vector A=4i+3j and B=5i-2j, how can I find the vector product AxB? I know that given the angle, its C=AB sin theta, but how can I solve this without the angle?
2
votes
2answers
903 views

Homework about spinning top [closed]

I have a top of unknown mass that has a moment of inertia $I=4\times 10^{-7} kg \cdot m^2$. A string is wrapped around the top and pulls it so that its tension is kept at 5.57 N for a distance of .8 m....
1
vote
1answer
233 views

Top spun up with string under tension problem [duplicate]

Possible Duplicate: Homework about spinning top I have a top with an unknown mass. It has a moment of inertia of 4.00 * 10^-7 kgm^2 a string is wrapped around the top and pulls it so that its ...
2
votes
3answers
3k views

Torque homework [closed]

We have learned that Torque is equal to a force that is perpendicular to a radius (displacement); however, I just cannot grasp one of the study questions we received: A hammer thrower accelerates ...
0
votes
1answer
5k views

Electric Field for a hollow sphere with point charge

I think I am over thinking this question: A point charge of $-2\space\mu C$ is located in the center of a hollow sphere. The internal and external radius of the sphere is given by $6.5$ and $9.5\...
1
vote
5answers
1k views

Conserved quantities in generalized n-body problem

Given a collection of point-particles, interacting through an attractive force $\sim \frac{1}{r^2}$. Knowing only $m_1a=\sum_i \frac{Gm_1m_i}{r^2}$ and initial conditions we can deduce the motion of ...
0
votes
2answers
7k views

Homework Help - Physics / Calculus III / Force-Work Problem [closed]

I have tried to answer the problem correctly, and I have found similar (and even an identical) problem in my textbook, yet I still can't seem to yield the correct answer with this specific problem. ...
2
votes
2answers
3k views

Mechanical energy problem

Question goes: "An anvil hanging vertically from a long rope in a barn is pulled to the side and raised like a pendulum 1.6 m above its equilibrium position. It then swings to its lowermost point ...
0
votes
4answers
305 views

Calculating electric field caused by 2 point charges [closed]

This problem is giving me a lot of problems. So $E=k*q/d^2$. We'd want to find the distance from q1 to P, which is .1 meters (not cm) using pythagorean thereom. So we know k, which is just $9x10^9$ ...