Rotatinal Kinetic Energy

A uniform marble rolls down a symmetric bowl, starting from rest at the top of the left side. The top of each side is a distance h above the bottom of the bowl. The left half of the bowl is rough enough to cause the marble to roll without slipping, but the right half has no friction because it is coated with oil.

My doubt is, once the ball enters to the smooth surface after rolling thro' the rough surface, what happens to the Rotational Kinetic energy?? I mean will it remain the same or it will be zero since there is no torque on the marble....

Answer1:

I think rotational K.E will convert in translational K.E and thus it will start slide over the surface and will move same distance

Answer2:

the rotational kinetic energy shall remain the same....the ball would be spinning with the same angular velocity when it reaches the top of the other end of the bowl....the only difference would be that it would now rise to a lower height than it was released from.

Answer3:

So it means "First the Potential energy is converted into KE and reaches the bottom of the bowl then since there is no torque on the marble it uses the KE to rotate the marble in the smooth surface and hence reaches lower height"...... Is my understanding correct??

Answer4:

no...the potential energy is first converted into translational and rotational kinetic energy as it reaches the bottom...then the translational kinetic energy is converted to potential energy as it goes to the other side...it reaches a lower height as the ball has not given up its rotational kinetic energy..and resumes the spinning

Why No Insulated Covering on Overhead wires running through the poles on the streets?

Question:

Our household wires all have insulated covering, using rubber, plastic or whatever it is. But the overhead wires running through the poles on the streets do not have any insulated covering. Explain.

Answer1:

It could be a way to save the finances, i guess

Answer2:

Reducing cost and reducing Electrostatic and magnetic coupling.

Answer3:

It's quite unlikely that someone would go up to a height of approximately 25 feet just to touch the wires. Moreover, if anyone touches the wires one would not complete the circuit. So there is least use of insulation.
While repairing, electrical supply is switched off.

Answer4:

The Great Transmission Line Theory

1. The wires running overhead do not have any insulating covering, ya it's absolutely true because in actual they don't need that.

2.Though the voltage carried by them is 230V to 4000V(in HV system), the separation is enough to produce very high impedance in order to avoid any coupling, also as someone said earlier the probability to someone touch that wire is also low.

3.Almost all such wires are made up of Aluminium, the conductor is having property of expansion, now if we put any insulator like Bakelite it may crack due to the expansion.
using rubber may solve the problem but then, the rubber too become hard due to prolong exposure to sunlight.

4. All connections made over such wires are just by warping another wire over them, as in Indian villages, so everytime removing that insulation will not be feasible.

5. Finally to conclude I would like to add... Addition of insulation does not add to the quality of transmission, ya it may prevent energy theft to certain point but the capital cost will be more than that. so the overhead transmission lines are normally not coated with insulation, but as in some crowded places they do cover them with pipes, or some insulation to avoid accidents.

Do You Agree?

is current really a vector??

OOps it should have been "is current really a scalar??"

it is generally considererd that current is a scalar qty because it doenst obey vector addn rules
but griffiths in his electrodynamics book argues u cant claim to be so esp when u go to a surface current or a volume current
the magnetic field produced by a surface current has a certain directional rel;ationship with that of the current
tell me who's right and who's wrong

where as i studied electric current is neither a scalar nor a vector quantity.Current in a wire when flowing has both magnitude as well as direction but since it doesnt obbey tringular rule . Also since it gives us the magnitude of charge flowing electrons per unit time is not related to direction at all

Current....in a sense can be argued to be a vector quantity. Afterall all, it's caused by a vector (magnetic/electric field)......the primarity mode of current is a vector (drift velocity of electrons).....but I'd say it's not a vector.......It basically has only 2 directions to flow in.....so naming the two directions + and - should abe about sufficent

The Green Tree catches fire, during Lightening...

We can't fire a green tree.... But, during Lightening, the green tree catches fire.... Why...? How is it possible....? Explain me in terms of Electrical charges or some other electrical terms.... Show your technical skill by answering this challenging question....

Answer1:

If we Starting d tree burning,,simply its very low Temp. compare to Lightening,,
& In case of Lightning Energy as equal to surface of sun strikes d tree for a 100 times less than a second ,,So water in d tree is convert into steam & steam spreads very rapidly ,,So Tree Become to catch firing easily.........&
Ofcourse bcs very High Temp. there is no more importance of green or yellow tree.......

Answer2:

Lightening's temperature is nearly 6273 K........ At this temperature, even iron will melt.... So.... Green leaf will get fried and toasted at this temp.... 

How do Earth get the Gravity?

please tell me if any one knows that,how did earth get gravity?

View1:

a great question...

you must have heard that earth behaves like a natural magnet...so it must have north pole and a south pole...
i just compare magnetic force as a gravitational force...
always earth will have its own field around it...
when you throw something up.. this force called gravitational force attracts it down towards the earth..

View2:

guys gravity has nothing to do with earth's core or its magnetic field. According to newton every partcle of matter attracts every other parlicle with the force which is directly praportional to product of there masses & inversly praportional to square of distance between them this is the gravity & we can feel the gravity of earth , moon , sun due to their great mass.

What do U think? Which Is Correct?

Toss a coin in the moving train

Question:

Toss a coin in the moving train.... does it fall in your hand back...?

Answers:

1.most probably no because ven train is moving ur position cahnges n the path of coin is parabolic n with respect to ur position it falls at the pt where u actually had been at the time of throwin the coin 

its basically a relativity question . ur relative position changes bt coin has a tendency to fall down straight

2.well the coin already have the x component of vilocity 
i.e vilocity of coin in x direction = vilocity of the train 

well just think of this small case when ur going to stadium to play cricket
while on the street ur tossing the cricket ball a lil up and catch it as u walk
u defnately just gave the ball its y component 
its x component was already the vilocity of ur walk

now think of another case while u go in ur car on a highway 
after having a can of soft/hard drink u throw it out of the window 
u see the can falls straight 
but no wrt to earth its parabolic it was straight wrt to u ... 
(u can notice this effect better if u can do it from a helicoptor)

so for every single mm u moved ahead it followed u 
u would see diffrent result if u suddenly apply break 
u will reamin at ur postion while the can will drop ahead of u


so the moral of the story is if train is moving on a smooth track u wud defenately catch the coin back 

acc to observer on earth the path of coin will be parabolic

acc to observer on train the path of coin will be straight

3.it depends on the velocity of da train . 

wen train is moving wid uniform velocity ,it falls back into hand .
'" "" " wid acceleration , it falls behind him . 
" " " wid decelration , it falls in front of him.

4.ya always...because here the train is the reference frame and you and your coin is in rest with respect to this frame

exceptions will take place if the train suddenly starts accelerating or deccelerating while the coin has alredy been tossed and its in air due to inertia

am i not correct?? close your eyes and just think virtuall as if u are on the train this practicehelps a lot in tackeling mechanics

5. Ummmmmm...... There can be three cases.... I assume that the condition is ideal... Then the three case can be.

(i) When the train is in Uniform motion, the coin will return to his hands.
(ii) When the train is moving with a unform accelration, the ball will fall behind him.
(iii) When the train is moving with a uniform retardation, the ball will fall in front of him.


Note : All the cases assume that u r facing the direction in which the train is moving.

What Happens If We Break The Laws Of Physics?

View1:

"Laws of Physics" are human attempts to understand the inner workings of the Universe.
The Universe itself and all its parts behave in predictable manner, each part in their own manner, ultimately resulting in the very reality we experience. We try to understand the different parts of the Universe and create algorithms to represent the manner in which each of its parts behave. We call these "laws of physics." These laws are mutable over time, as new understanding of how the different parts of the Universe behaves constantly requires us to review established knowledge. 

Ultimately however, regardless of our understanding, the actual way the Universe behaves remains the same and immutable.

You see, the behaviors preexist our understanding of these behaviors; moreover, they preexist human beings (not just in the sense of time, but in the sense of space, that is, the sum of these behaviors is what allows for the existence of human beings as we know it.)

We are, in a way, a "behavior" within the Universe, and being that we're only a part of it, we can't change the whole thing, we can only change ourselves, hence what we call free will.

View2:

The laws of physics are laws of nature

dera all, the laws of physics are the laws by which

 natural forces

 work. we and all our creations including all the computers and equipments are made and created by following the same laws. there is no way that the laws can be broken unless they are in first instant not universal. say for example the laws of motion as predicted by Newton no longer hold good in nano world and in relativity concepts close to speed of light. we can not do anything that nature does not have in built in its existance. yes we can imagine against law of physics. most of holywood films do it as routine. but whetever they show follows the laws of nature in creating it. including digital manuplation.

What Do You Think?