Resolution of Vectors

From: Vakas
Subject: Resolution with geometry
Message Body:
Dear sir,
I m not able to understand that when we resolute mg in a inclined plane that plane having angle theta,how does the vertical component goes through inclined surface & cos comp opp to N.
explain with geometry so that i don't get confused in future in determining the two comps is right direction.
Ans:
In a right angled triangle,

and

When mg is resolved into mutually perpendicular directions, one parallel to plane and the other perpendicular to the plane (opposite to the Normal reaction), the component which is adjacent to θ is the cos component and the one away from θ is the sine component.
Students find difficulty ,mainly in identifying the angle .
See the diagram below and try to analyze

Questions from Properties of gases

Senarita asked:

“we know that temperature has a properties to make some thing bigger in volume.we say that gas has no particular volume or shape.where we place a gas it takes the shape of that container.my question is- a gas of mass 'm' has a particular number of atoms or molecules.if the gas is not getting any temperature then how it is occupying all the volume of a bigger container.i mean how the inner space of two atoms or two molecules of that particular gas is increasing when i am transferring it to a bigger container.(say,every condition is constant.nothing is changed.)please answer me.”

can you give me some name of sites where i can get explanations on hydrostatics or the topics of physics.i am now in class 11

Master will be answering the question shortly. The visitors are requested to respond

A Question from Electromagnetic Waves

Rajat asked: - we know that electric and magnetic field are associated with charged particle but when light travells,it produces electric and magnetic field both but it consests of photons,which is a uncharged particle.why it did so? Master will soon answer this. By the time, if any visitor wants to answer, please use the commenting system

A question from kinematics - motion in one dimension

Natasha Sehgal Asked:

"A stone is thrown in a vertically upward direction with a velocity of 5m/s. If the acceleration of the stone during its motion is 10m/s^2 in the downward direction , what will be the height attained by the stone and how much time will it take to reach there?"

Answer: Take, u=5m/s a= -10 m/s² v=0 at the topmost position S= H_max = ? The eqn of motion to use v² - u² = 2aS Which gives H = 1.25 m From the eqn v=u + at t= 0.5 s

Find time of death of patient with differential equations

Mr. N.P. Sahani asked:

"The differential equation and solution for finding the time of death of a patient"

Answer:

See that the question is to find the time of death (Not predicting the time of death. I thought that when I read it first.)

I can give some links which will be helpful in this connection

1. http://www.exploreforensics.co.uk/estimating-the-time-of-death.html
2. http://en.wikipedia.org/wiki/Thermal_death_time
3. http://autarkaw.wordpress.com/2008/07/21/time-of-death-a-classic-ode-problem/
4. http://people.uncw.edu/lugo/mcp/DIFF_EQ/deproj/death/death.htm
5. http://mathforum.org/library/drmath/view/53409.html
6. http://www.scribd.com/doc/21514655/Newton-s-Law-of-Cooling-Finding-the-Time-of-Death-of-a-John-Doe

Resistance and Resistivity

Simran Asked

"Two wires A and B of equal lengths,different cross-sectional areas and made of same metal a)name the property which is same for both the wires. b)name the property which is different for both the wires"

Answer:

Since both the wires are of same metal, the resistivity will be same for both whereas since the dimensions (Area of cross section here) are different, the resistance will be different

Potential Difference

Pawan Asked

"What is meant by potential difference?"

Answer:

"Potential Difference between two points is the difference in Potential between the two points and is equal to the work done per unit charge ion carrying a positive test charge from one point to another against the electric field and without any acceleration"

Limitations of Homogenity

Paraser asked

"What are the limitations of homogenity?"

The question is acutually"What are the limitations of dimensional analysis?" The dimensional analysis is based on the principle of homogenity of dimensions. The question is already discussed earlier  HERE

Geothermal Energy

p.tejaswini asked

"Why is geothermal energy an alternative source of nuclear energy?"

There is some problem with the doubt you asked. It is correct to say "Geothermal energy and Nuclear energy are alternative sources of energy" Sun is the ultimate source of energy for earth. The energy of fuels, wind energy, water energy, food - all these are derived from sun. But Geothermal energy and nuclear energy are not derived from solar energy. GeoThermal Energy Links for Reference http://www.renewableenergyworld.com/rea/tech/geothermal-energy http://www.geos.iitb.ac.in/geothermalindia/pubs/geoweb.htm See a diagram of Geothermal plant [caption id="" align="alignleft" width="525" caption="Geo Thermal Energy"][/caption] The centre of the Earth is around 6000 degrees Celsius - easily hot enough to melt rock. Even a few kilometres down, the temperature can be over 250 degrees Celsius if the Earth's crust is thin. In general, the temperature rises one degree Celsius for every 30 - 50 metres you go down, but this does vary depending on location In volcanic areas, molten rock can be very close to the surface. Sometimes we can use that heat. Geothermal energy has been used for thousands of years in some countries for cooking and heating. The name "geothermal" comes from two Greek words: "geo" means "Earth" and "thermal" means "heat". Read More on Geothermal Energy Here

End of Universe ; Vishnu says

last day i saw a prog in natgeo
"How universe ends?"

it presented 2 theories
one says
the universe expands expands expands
everything splits and expands
at last
molecules splits to atoms
and no more molecules exist
only isolated atoms
it will be cold and dead
thats the death of universe
then somehow an atom gets excited
it collides with another
thus a point of hier gravity created
everything pulled into it
and everything joins
then another
BIG BANG
thats one theory
the next says
universe expands to a limit
then its energy runs out
and falls back
thus contraction of universe
contracts contracts contracts
to a
Singularity
then another
BIG BANG
new universe
these are the 2 theories they speak of
the first one got more weightage
since the expansion of universe is accelerating

second one happens only if it decelerates

it is determined by the amount of dark matter and dark energy we have
if dark matter is more, then the contraction theory comes true.else the expansion.