## A General Quiz on Physics

Attempt this online quiz to check your knowledge of the basic concepts and fact of Physics. The quiz is being developed. You can finbd more and more questions added to it when you come back to this page later.

[mtouchquiz 3]

## Big Bang and some thoughts on it

John Reynolds posted: –

Setup- lately I’m partial to the idea that our universe originated from a black hole in another universe. I know this idea has been offered before, but I don’t know how reputable or not it is among physicists. It seems to make sense- black holes end and the big bang began, with a singularity, a place where the laws break down and parameters approach or equal infinity. While evidence from other universes or beyond singularities may be unobtainable, even in principal, several popular mathematical models support a multiverse. So the question is- does anyone have a good reason, other than lack of evidence, to doubt the hypothesis that our big bang was another universe’s black hole?

## Stability of inverted catenary arches

Sir, I have to submit a paper tommorrow on the types of arches. I am permitted to use the web. I heard that the most stable arch is the inverted catenary arch. But even after surfing for hours I didn’t get the physics hlvehind it. Please explain how can I prove it is the most stable curve. Please do help as soon as possible.

Posted Muralikrishnan A

Answer:

In physics and geometry, a **catenary** is the curve that an idealized hanging chain or cable assumes under its own weight when supported only at its ends. The curve has a U-like shape, superficially similar in appearance to a parabola, but it is not a parabola: it is a (scaled, rotated) graph of the hyperbolic cosine. The curve appears in the design of certain types of arches and as a cross section of the catenoid—the shape assumed by a soap film bounded by two parallel circular rings.

The catenary is also called the **alysoid**, **chainette** or, particularly in the material sciences, **funicular**

Please visit

https://en.wikipedia.org/wiki/Catenary#Inverted_catenary_arch

for some details

More links to refer:

http://mathworld.wolfram.com/Catenary.html

http://xahlee.info/SpecialPlaneCurves_dir/Catenary_dir/catenary.html

## Mechanics Doubt

Question: A parent holds a small child in a swing so that the angle of the swing support is at 20 degrees to the vertical. The child’s weight is 200N and the swing seat weighs 50N. What horizontal force must the parent apply?

The answer provided in the textbook is 72.8N, but I’ve been struggling to get the same answer as I’m rather confused by the wording of the question and so I can’t really picture how the situation in the question would look like. Thank you in advance.

Asked Tanacha

## Problem from Kinematics

Tom is initially 6.0km west of a flagpole and running with a constant velocity 9.0k/h due east.jack is initially 5.0km east of the flagpone and running with a constant velocity of 8.0km due west. What will be the distance of the two runners from the flagpole when their paths cross?

Asked Shang

## Difference between trsnsmission and refraction of light

Please tell me ,refraction is dimply bending of light ,when itvtravel from one medium yo another, I have a doubt , what exactly happens in transmission of light ,Is this refraction of light in the same medium, please explain me it in detail, thank you very much

Posted Beverly Alcock

## Activity and Half Life

If an 8000Bq source of activity has a half life of 6 days, How much activity will it have after 18 days. I know the answer is 1000Bq but could you explain how you got it very clearly?

2nd question. Calculate the half life of a source that decreases in activity from 32kBq to 8kBq in 24 days. Could you explain that clearly too? Thanks.

Asked Adam