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 questions.

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0
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1answer
23 views

Weight held by jet stream of water

Consider a bucket of weight $W$, held in air by a jet stream of water from the ground (moving vertically upwards) at height $h$. The water is fired from the ground at the rate of $\mu$ (units ...
5
votes
1answer
129 views

Force problem related to adhesive and bonding

I have two PCBs (printed circuit board), and they are glued by adhesives, as show in the pictures. And the location of the adhesives are indicated on the picture (please notice that NO adhesive is ...
0
votes
1answer
38 views

Magnetic field above center of current-carrying loop

A current $ I = 2A $ flows in a circular loop coil of radius $R = 10 cm$. Evaluate the magnitude of the magnetic field (in Tesla) at a point $P$ on the axis of the coil, and a distance $z=5cm$ away ...
2
votes
1answer
144 views

Is work is equal to $mv^2$ (without $\frac{1}{2}$)?

I was trying to come up with an equation for work that doesn't include time, because I don't know time. Here's what I did: $$ work = Fd = mad = m{v\over t}d = m{v\over\left({d\over v}\right)}d = ...
0
votes
1answer
27 views

Calculating deceleration from a non-constant force [on hold]

As a background : I am trying to design a spring to locate at the end of a zip-line (flying fox) to decelerate a person slowly. I am having some trouble working out the deceleration because it ...
0
votes
0answers
17 views

Tension on two string with one known angle and one known tension [on hold]

Consider a 50-N weight suspended by two wires as shown in the accompanying figure. If the magnitude of vector F1 is 35 N, find angle alpha and the magnitude of vector F2
0
votes
1answer
18 views

Gravitational Potential Energy to Kinetic Energy

When a yo-yo is released from a height $h$, the gravitational potential energy is converted to kinetic energy. However, the yo-yo obviously has less acceleration than $g$, $9.8\frac{m}{s}$. This means ...
1
vote
1answer
1k views

The electric field of a conductive sphere containing a charge - grounded vs not grounded

Let's suppose we have a sphere but unlike theoretical ones it'll have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge $q$ ...
1
vote
0answers
38 views

Show that the profile of the hill is a cycloid [on hold]

I'm struggling with this problem: From George Simmons_ Differential Equations I've tried different things and I showed that the $x$ component and the $y$ component of the shadow should move with ...
3
votes
5answers
319 views

Commutator algebra in exponents

Considering $X$ and $Y$ such that $[X,Y]=\lambda$, which is complex, and $\mu$ is another complex number, prove: $$e^{\mu(X+Y)}=e^{\mu X} e^{\mu Y} e^{-\mu^2\lambda/2}$$ My attempt (so far) is: ...
4
votes
3answers
103 views

Different results to a basic question ( Newton's law and perservation of momentum)

Trolley with mass of $m_0=1 \ kg$ is moving without friction on the railway track. It is raining so there is a constant mass flow of water $\Phi_m=0.1\ kg/s$. Constant force $F=0.1 \ N$ is ...
0
votes
3answers
39 views

Distance covered - variable acceleration [on hold]

Question: A point moves in a straight line under the retardation $av^2$, where $a$ is a positive constant and $v$ is speed. If the initial speed is $u$, the distance covered in $t$ seconds is: a) ...
3
votes
4answers
201 views
+50

How can I calculate the force that is applied on a tube by another tube?

Let's say there is two tubes(cylinders with no tops or bottoms) with charges $q_1$ and $q_2$, radii $b_1$ and $b_2$, lengths $l_1$ and $l_2$. These tubes are located along the axis of each other's ...
3
votes
0answers
26 views

Equivalent Dose absorption from Na22 source

No idea what exactly the rules are or how I should ask this question, but here's the verbatim quesiton: "A Na$^{22}$ source has an activity of 100 $ \mu $C. If you handle the source, how big is the ...
5
votes
6answers
8k views

What would be the effective resistance of the ladder of resistors having n steps

I'm a tutor. This is a high school level problem. In high school, every one have might have solved a problem of effective resistance of a ladder of resistors having infinite steps. Now the problem is ...
1
vote
2answers
32 views

Followup to: The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity

As a followup question to this question: The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity and this answer ...
0
votes
1answer
69 views

What distance does one travels in his lifetime? [on hold]

I think this isn't answerable without having point of reference from which speed at which earth travels in space, however if I am wrong the please give absolute distance. Considering that earth spins ...
0
votes
0answers
55 views

How many atoms make up the average ant? [on hold]

Given an ant is anywhere from three to five milligrams,
1
vote
2answers
1k views

Finding max height of a mass launched by a spring?

I have the following problem on my homework. The actual problem has numbers, but I figure using symbolic notation will help me understand the concept in the long run. A block of mass $M$ is launched ...
0
votes
0answers
17 views

Solving for currents in a circuit [on hold]

I need help finding the three listed currents in the figure below. Attached on the bottom is the solution for this problem, however I do not quite understand how they came up with the answers. ...
-1
votes
1answer
32 views

equivalent spring constant for a nonlinear spring force [on hold]

The force-deflection relation of a steel helical spring used in an engine is found experimentally as $F(x) = 200x + 50x^2 + 10x^3$, where the force $(F)$ and deflection $(x)$ are measured in pounds ...
1
vote
0answers
20 views

Unsure how resistors are connected? (Series/Parallel) [duplicate]

I am currently attempting this practice question in my tutorial and while I am able to reduce the circuit below to I do not know whether the 6/6/6/6 pane is connected in series or parallel, it ...
0
votes
1answer
21 views

A Conversion problem featuring Significant figures [on hold]

What is the speed of a car going v=1.000 mile per hour in SI units? You can do each conversion separately. Use the facts that 1mile=1609 meters and 1hour=3600 seconds. Express your answer in meters ...
1
vote
1answer
38 views

Resistors in para and series circuit, finding volt [on hold]

How anyone know how to do the question? I know how to reduce it to a window pane of 6/6/6/6 with a 3 in series but i have no idea how to do it. Well i did manage to reduce the right side of the ...
3
votes
1answer
266 views

Semiconductor problem: how much Boron is required to establish a certain amount of charge carrier density

The problem description is as follows: Boron is used to dope 1 kg of germanium (Ge). How much boron (B) is required to establish a charge carrier density of 3.091 x 10^17 / cm^3. One mole of ...
0
votes
1answer
44 views

A moving inclined plane with block problem

I'm trying to solve for a challenging problem : a moving inclined plane with a block I want to solve for the acceleration components for the block and the plane and the normal force acting on the ...
-4
votes
0answers
21 views

Capacitance of air capacitor [on hold]

Hi I'm currently working on the following question (image below), any help is much appreciated!
0
votes
2answers
40 views

equivalent spring constant for a drum floating in water

If I have a drum floating in water, how do I find the equivalent spring constant? I know that the water has density $\rho$, the drum has diameter $d$ and height $\ell$, and the positive direction is ...
6
votes
1answer
215 views

Is it possible to determine particles' velocities from their crossings on a ring?

2 particles are constrained to move in a ring. Both particles begin moving at $t=0$ from $p=0$, each particle moving in the opposite direction of the other. It is known that they are moving at ...
0
votes
1answer
31 views

Deviation from 2D trajectory

I need to find out how far a ball is from the predicted trajectory in 2 dimensional space and I know the start and end position of the ball in both dimensions. Along with that I know the initial ...
5
votes
2answers
325 views

The acceleration vector of a simple pendulum

In this picture the acceleration vector $\vec{a}$ points upward when the pendulum is halfway Click To see animated GIF But according to this picture, the force acts tangentially: Which means the ...
1
vote
1answer
95 views

Magnification of an astronomical telescope not in normal adjustment?

I am stuck on this question: A telescope consists of two thin converging lenses of focal lengths 100cm and 10cm respectively. It is used to view an object 2000cm from the objective. What is the ...
-3
votes
0answers
27 views

Solve the following linear second order circuit [on hold]

I am not able to solve for the second part of the question (when v(t) = 0)
-2
votes
2answers
60 views

Unit conversion from km to mm [on hold]

I'm a bit rusty on my unit conversion skills and I need help figuring out what I did incorrectly converting 9.06 x 10^8 km into mm. Here's what I did: 9.06 x 10^8 km x (1 meter/10^3 km) x (10^-3 km/1 ...
0
votes
0answers
57 views

Differential Equations [on hold]

$$ \nabla^2 B = - \mu_0^2 \epsilon_0^2 \frac{\partial B}{\partial t} $$ $$ \nabla^2 E = \mu_0 \epsilon_0 \frac{\partial B}{\partial t} $$ Find as many E and B field solutions as you can from this. ...
3
votes
1answer
108 views

Forces acting on two balls in a jar [on hold]

Consider the following situation: Two balls are inside a jar with diameter $D$. The balls are uniform in mass and both have the same diameter $d$. Express the forces that acts at the colored dots ...
0
votes
0answers
19 views

Calculate object displacement with a radial/centripetal acceleration [on hold]

What i want to do is calculate the displacement of a object with a certain radial acceleration in a moment of time. The object has a velocity, radial acceleration and a tangential acceleration. For ...
-2
votes
1answer
30 views

What formula connects the moment of inertia and angular velocity? [duplicate]

I need to determine angular velocity of a disc when a man with given mass and speed whacks on the edge of it. I calculated the total moment of inertia of disc and body, how do I calculate the ...
1
vote
1answer
60 views

An oscillating skateboard

A half pipe of a skateboard park consists of a concrete trough with a semicircular section of radius 5m, I hold a frictionless skateboard on the side of the trough, pointing down toward the bottom and ...
0
votes
3answers
40 views

Perceiving travel speeds from different view points

Scenario: Two vehicles pass each other on a highway moving at 100km's an hour; from a stationary position beside the road you witness these cars pass each-other directly in front of you: from your ...
0
votes
1answer
20 views

Torque due to a magnetic field

We have two infinite perpendicular wires, each carrying a current "i" and the distance between them is l. If both the wires are free to move, how will they arrange themselves because of the torque ...
0
votes
0answers
30 views

How do charges actually distribute among capacitors? [on hold]

Two capacitors of capacitance $3 \mu F$ and $6\mu F$, are charged to potentials of 2 V and 5 V respectively. These two charged capacitors are connected in series. Find the potential across each of the ...
1
vote
0answers
107 views

Textbook disagreement on geodesic deviation on a 2-sphere

Apologies if I have this completely wrong (and for the general long-windedness). I've searched online but can't find anything helpful/relevant. I'm trying to use the geodesic equation ...
2
votes
1answer
35 views

The relation between energy quanta of an Einstein solid and the equipartition value of heat capacity

Consider an Einstein solid with quantized energy values $U=q\epsilon$ and $N$ oscillators. I calculated some values of an Einstein solid numerically through a function in R (at the bottom of the ...
1
vote
1answer
84 views

Rotation and fictitious forces

A bug eats through an apple and forms a vertical, infinitesimally thin canal parallel to the vertical diameter at a distance $\frac{R}{2}$ from the center. The apple rotates at angular velocity around ...
0
votes
0answers
28 views

electrical potential [on hold]

The electrical potential at a distance r from a point charge, Q, is given by the function $$V(r)= \frac{Q}{4 \pi \epsilon_0 r}$$ (i) What is the gradient of this function? (ii) What is the ...
0
votes
1answer
160 views

Absolute Viscosity of Water at certain temperatures

I just started my class on fluid mechanics. There's a problem that requires absolute viscosity $u$ of water at 25C. I looked up my table in the book and I only have it for water at 20C and 30C. I ...
-2
votes
0answers
42 views

Electricity Problem [on hold]

A power Station Is Connected To A Factory 2.5 km Away By Two Wires the potential difference between the terminals of the wires at the station is 240v and that for the other terminals at the factory ...
4
votes
3answers
2k views

Pluto's gravitational pull on a person on the Earth's surface?

My Physics teacher stated that Pluto has a gravitational pull on objects on Earth, namely humans. Is this true? What is the free-fall acceleration of Pluto with respect to being on the Earth's ...
0
votes
0answers
44 views

Infinite Atwood (pulley) system - what's wrong with this? [on hold]

Each block has mass $m$. We are finding acceleration of topmost block. Assume the tension $T$ acting on topmost block and acceleration $a$ in upward direction. Then tension on second block is ...