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Electrical Potential question

We have been given practices tests with answers and I have been at this for hours and I can’t get the same answer that my teacher has given us which is:
Ez= -(100z + 100/z^2)

I have tried this every which way and can’t get it.

The electric potential along the z-axis is given by
V(z) = 50 z2 V/m2
– 100/z Vm,
where z is given in meters. Give an expression for Ez(z).


Posted by James Malone

Measuring Exact Wavelength in Lab

Hi, I need a software or an apparatus (available in school conditions) to measure wavelengths of visible light. In my lab I use coloured filters to get different colours of light, but I have to measure exact wavelengths.
Thank you in advance


Vanja posted


The wavelength may be measured by Diffraction grating experiment, Newton’s rings experiment etc.



Big Bang singularity

Does a singularity contain mass?? if yes then according to big bang , our universe sprang into existence as “singularity” around 13.7 billion years ago. it means there was already a mass centered in zero volume.

and only a black-hole has singularity it means at the time of big bang there was a black hole in which explosion occurred.
please guide me and give me ans.


Asked Shyam



The word singularity means

“the state, fact, quality, or condition of being singular.”

“a point at which a function takes an infinite value, especially in space–time when matter is infinitely dense, such as at the centre of a black hole.”

” a point at which the derivative of a given function of a complex variable does not exist but every neighborhood of which contains points for which the derivative does exist”

Evidently, singularity refers to a unique situation, in big bang whatever state of affairs triggered contributes to the singularity.


Refer to



Did The Universe Really Begin With a Singularity?


Velocity and Displacement – A different Perspective

A person is born on point A and dies on point B, point A = point B. What is her/his average velocity?

I know that the answer should be 0, but is there any possibility for the person’s average velocity to be any number that isn’t 0? Her/His displacement is 0, so her/his average velocity should also be 0, but I have people arguing that it is possible for the person’s average velocity to not be 0, or that there is not enough information provided in the question to solve for the answer.


Posted by Jack


If you consider with respect to earth only, then the answer is zero. But if the point of reference is outside the earth, then the answer will be different. If the frame of reference is outside the solar system, or milky way galaxy then the answer will be different again.


Roller Coaster Physics

There is a species of bug on the planet Mindbender called bugonians than can only hear over the frequency of 290Hz. Bugonians are blind and relies only on hearing to survive. The mass of Mindbender is 7.66 x10^25 kg and a radius of 2.46 x10^7m.
A pendulum with a frequency of 0.41Hz attached to the ceiling above the top of a miniature rollercoaster. The bob on the pendulum has a mass of 2.0 kg. It hits a toy cart with a weight of 4.0N at the top of a track, which is touching a spring, with a spring constant of 2.6N/m. It is positioned 0.15m from equilibrium when it rolls down the hill.
The height of the first hill is unknown, but it is equal in height to the first loop of the rollercoaster. The minimum velocity to keep the cart in the first loop is 1.656 m/s.
After the first loop, the cart moves up a ramp with a coefficient of friction of 0.009. The cart is producing a noise at the frequency of 250Hz. The ramp has a height of 0.20 m, where it drops off and the cart is launched as a projectile.
There is a Bugonian suntanning 4.6m from the end of the ramp. Can the Bugionian hear the approaching cart, if you consider the Doppler effect on the frequency of sound as the cart is hurdling through Minderbender space towards him?
You must assume complete energy conversions UNLESS there is friction

Posted by Sam

A thought provoking and creative question from kinematics 

You are arguing over a cell phone while trailing an unmarked police car by 25.0 m; both your car and the police car are traveling at 120 km/h. Your argument diverts your attention from the police car for 2.0 s (long enough for you to look at the phone and yell,“I won’t do that!”). At the beginning of that 2.0 s, the police officer begins braking suddenly at 5.05 m/s2. (a) What is the separation between the two cars when your attention finally returns? Suppose that you take another 0.500 s to realize your danger and begin braking. (b) If you too brake at 5.05 m/s2, what is your speed when you hit the police car?

Posted by Fardhokt

Relative velocity

F​rom: nileshnegi

Subject: kinematics

Message Body:
on a 2 lane road,car A is travelling with a speed of 36 km/hr 2 cars B n C approach car A  in opposite direction with a speed of 54km/hr each. at a certain instant when distance AB is equal to AC both bieng 1 km.. B decide to over lap A before C does . what minimum of acc of car  B is required to avoid an accident with car A?

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