IIT JEE , AIEEE Forum - Physics , Mechanics

ridhima

since most of us have finished

mechanics , especially the

+1 students who have it fresh

in their minds . let us try to

make our concepts more

better .

most of us must have faced

this problem of judging the

problem in the wrong way

let us compile all these

common errors and post it

here so that every1 can

benifit fron it

5 pointer to every

contribution cheers

ridhima

com on we all will benifit from it

rates assured

ridhima

HEY ROONEY
BIPIN WATERDEMON
CHIMANCHU
DEE DEE
COM ON
CONTRIBUTE

waterdemon

Yes you are right but if you would have asked about what
are the important concepts for Mechanics then you would
have had number of replies till now.
But As you have asked about the "Errors" that we come
through so it is a bit difficult for re-collecting it back :)

Anyways I am submitting one as it is a genuine one :

1)If a body is in Equilibrium then it does not mean that no
Forces acts on the body but it simply means that the net
Force on the body is Zero.

Hope it is useful.
Will post more if remember them.
Cheers!!!!!!!!!!!!!

ridhima

YA GR8
THINK OVER IT U'LL SURELY GET MORE ANSWERS
GUD JOB
MORE REPLIES AWAITED

ridhima

OK HERE'S ONE FROM ME

IF A BODY IS ROLLING ON

A ROUGH SURFACE AND IT

ENTERS A

FRICTIONLESS SURFACE

THEN MOST OF US MIGHT

THINK THAT ROLLING

WILL NOT CONTINUE

AS THERE IS NO TORQUE

OF FRICTION

BUT

REMEMBER THAT DURING

ROLLING THE POINT OF

CONTACT IS T REST

SO NO FRICTION WILL ACT

NOW EVEN IF IT ENTERS THE FRICTIONLESS SURFACE IF WILL

CONTINUE 2 ROLL

CHEERS

waterdemon

Some important points in "Collisions" that we generally
ignore and make mistakes without knowing the meaning
of them:

1)Line of Impact:

When two bodies collide, their surfaces are in contact while
collision.If a line is drawn perpendicular to the common Tang
ent to the surface at the point of contact,the line is called
as "Line Of Impact".

2)Direct Impact:

When the centres of mass of the colliding bodies r initially
moving along the line of impact,impact is called as "Direct
Impact" or we say it "Head on Collision".It should be known
that after " Direct Impact " bodies continue to move along
the "Line of Impact".

3)Oblique Impact:

When centres of mass of the colliding bodies are not moving
initially along the line of Impact, then the impact is called
as "Oblique Impact".

Hope it is useful.
Cheers!!!!!!!!!!!!!

ridhima

GUD WORK WATERDEMON
REALLY USEFUL

ridhima

MORE REPLIES AWAITED

waterdemon

What I am giving now is not there in HC Verma:

Semi-Elastic Collisions:

The Collision that falls between Perfectly Elastic & In-Elastic
Collisions are called as "Semi Elastic Collisions".

In these collisions part of the total KE is Lost during Collision
i.e K.Energy is not conserved although the total Energy is
Conserved

One more point to be known in this is that the loss of K.E
in such collisions is not sufficient for the bodies to stick
together as in case of "Perfectly In-Elastic Collisions".
Here the principle of Conservation of momentum holds.

Consider two bodies of masses 'm' & 'M' moving with Vel.
U₁ and U₂ and collide each other.Let their Velocities be
then V₁ and V₂.

For Semielastic Collision we have:

e = V₂ - V₁ / U₂ - U₁

Hope it is useful.
Cheers!!!!!!!!!!!!!! :)

waterdemon

Some more important points to be remembered:

We very well know that:

= rFSin@

And when Torque is a "Vector"

= r x F

Now,
1)For a goven Force, the torque is maximum when r is max.
For example, it is easier to close / open a door by applying
the Force at the edge of the door rather than at middle
or somewhere else.

2)Torque is max when Sin@ = max that is when @ = 90.
When Force is applied in a direction perpendicular to "r".

3)Torque is "Zero" when @ = 0 / 180.
For example the door can be rotated by applying a Force
in a Direction parallel to the plank.

Hope it helps.
Cheers!!!!!!!!!!!!

siddharthsaxena

i would lyk 2 bring forward one of the most common mistake by students in WORK ENERGY AND POWER

In elastic collisions, total energy remains same throughout the time of contatc

but the kinetic energy doesnt ( some of it gets converted into potential energy and back to kinetic during collision)........

Rate me if useful..............

tka

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