# Search results

1. ### Modulus of the electric field created by a sphere

I think the right solution is c). I'll pass on my reasoning to you: R=6\, \textrm{cm}=0'06\, \textrm{m} \sigma =\dfrac{10}{\pi} \, \textrm{nC/m}^2=\dfrac{1\cdot 10^{-8}}{\pi}\, \textrm{C/m}^2 P=0'03\, \textrm{m} P'=10\, \textrm{cm}=0,1\, \textrm{m} Point P: \left. \phi =\oint E\cdot...
2. ### Origin of potentials

I think the right choice is c. I'll pass on my reasoning to you: We can think that if the formula of the potential is V(r)=\dfrac{kq}{r} If r tends to infinity, then V(r)=0. But the correct answer is d).
3. ### Potential at a point

I thought the right choice was d). But when it comes to the solutions, it is b) and I don't understand why. My reasoning would be: the potential at a point is the work that the electric field does to transport a charge from infinity to that point, so if the field is zero, it does no work and...
4. ### Capacitance of a spherical capacitor

When I try to do Gauss, the permeability is not always that of the free space, but it varies: up to a certain radius it is that of the void and then it is the relative one. How can I relate them? I'm trying to calculate the capacity of a spherical capacitor. The scheme looks like this: inside I...
5. ### A rocket and its gas exhaust velocity

This isn't right, is it? -\dfrac{GM}{R}+\dfrac12 v^2=-\dfrac{GM}{R+h} v=\sqrt{\dfrac{GM}{R}}\left( 1-\sqrt{\dfrac{R}{R+h}}\right) He's doing energy conservation. The mechanical energy at the Earth's surface is equal to the energy when the speed is 0.
6. ### Electric field and electric potential exercise

a) \vec{F}=\vec{E}\cdot q \phi =\oint \vec{E}d\vec{S}=\oint \vec{E}d\vec{S}=\underbrace{\oint \vec{E}d\vec{S}}_{\textrm{FACES } \perp}+\underbrace{\oint \vec{E}d\vec{S}}_{\textrm{FACES } \parallel}=0+\oint EdS\cdot \underbrace{\cos 0}_1= E2S \dfrac{Q_{enc}}{\varepsilon_0}=\phi \left...
7. ### Determing the center of gravity of a shaded section

Determine the volume of the shaded area around the Y-axis by using the theorem of Pappus Guldinus, where value of R = 143,3 cm. a) Determine the area of the shaded section. b) Determine the center of gravity of the shaded section. c) Detrmine the volume by using the theorem of Pappus Guldinus...
8. ### Determining a centroid

Summary:: I'm solving an exercise. I have the following center of gravity problem: Having the function Y(x)=96,4*x(100-x) cm, where X is the horizontal axis and Y is the vertical axis, ranged between the interval (0, 93,7) cm. Determine: a) Area bounded by this function, axis X and the line...
9. ### Gauss-Theorem on a solid dielectric sphere

The load system formed by the point load and the load distribution generates two regions in space corresponding to r<1m and r>1m, i.e. inside and outside the sphere. Given the symmetry of the distribution, by means of the Gaussian theorem we can find the modulus of the field at a distance r from...
10. ### Electric dipoles

What is the convention? Because the field lines leave the positive charges and enter the negative ones, do not they?
11. ### Applying a force in a wheel bicycle

Homework Statement We have a bicycle and lift the front wheel. And with the hand we apply a force of 10 N down and we turn the wheel. The wheel is 26 inches in diameter and weighs 1.5 kg. Find the angular acceleration, the torque of the net force and the angular velocity after a lap. Homework...
12. ### A transmission system exercise

Homework Statement We have a transmission system (plate-pinion), with a 38-tooth chainring and a 14-tooth sprocket. The distance between the crank (between the chainring and the pedal) is 170 mm and the pedal is overloaded with 60 kg and pedalled at a speed of 70 min-1. Homework Equations P =...
13. ### Sign of the Faraday-Lenz equation

Homework Statement Hello, good afternoon, I have a question that's coming up when I'm doing electromagnetic induction exercises. In some exercises they ask me to determine the electromotive force (iee), and when they do the exercise resolution they do it with absolute value. In other...
14. ### A Kirchhoff problem: Find the currents and voltages in this circuit

Homework Statement In the circuit of the figure, determine the intensities I1, I2, I3, I4, I5 and the voltage Ug. Homework Equations Superposition and Kirchoff The Attempt at a Solution 20-10I1+5I3-10I1=0 5I3+Ug+5I5=0 20I2+10I2-150=0 From the last equation, 30I2 = 150, I2 = 5 A KNOTS...
15. ### The phase of a simple harmonic motion

Homework Statement How can I calculate the initial phase in a simple harmonic motion if I only have the amplitude, frequency and angular velocity as data? Homework Equations The formula of the position, in fact they ask me to do the formula that allows to know the elongation depending on the...
16. ### Displacement given the acceleration

Homework Statement How could I get the distance traveled by a vehicle having only its constant acceleration as data? Homework Equations I know that the acceleration is the derivative of the velocity and the velocity is the derivative of the position. The Attempt at a Solution I don't know how...
17. ### Potential of an undefinided cylinder

Homework Statement Determine the potential that creates an undefined cylinder of radius $R$ and density density $\rho$ that is uniformly charged. Homework Equations Gauss's law. The Attempt at a Solution I know that for this problem I can use gauss because it is a cylinder, now I do not get...
18. ### Can Gauss' Law be used to calculate the electric field generated by a uniformly charged thread?

Hello, Can not Gauss's Law be used to calculate the electric field generated by a uniformly charged finite thread? I suppose it is because I can not consider the electric field constant (always going to the same direction), and for this I would have to do it by parts (the lateral flow, and the...