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 This Post 10 points    (2    in 2 votes )   [?]

Look at the video below. Pranav Mistry a student of MIT has done some amazing inventions. He is an M Tech from IIT Bombay and is a Ph D student at MIT. He did his B Tech from Gujarat. It is worth seeing.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

It is true, the best IIT is in which the best students join. By that yardstick IIT Bombay is the best. IIT Delhi comes next.

IIT Bombay attracts more than 50% of students from top 100 JEE rankers!!!

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

Avinash_Bhat is right. If you can seal the surface perfectly by some means there will be no buoyancy force on the body. Instead there will be a downward thrust  equal to area* height of water column above the body*density of liquid. This thrust will be felt on the floor as well.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

Is it possible to rotate a stone tied to a string in horizontal circle? Always there will be an inclination with respect to horizontal to accommodate the force of gravity! So 'mg' also will have to be considered. In such case as we accelerate the speed of rotation the inclination will come down and stone will rise. Problem becomes complex.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

80% aggregate is too much for IITJEE eligibility. I suggest 80% in PCM and 60% aggregate. Otherwise rural students will find it difficult. There is no reason why a student who clears JEE cannot score 80% in PCM.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

In case of bullet , the shear stress created is sufficient to rip off the glass due to high impulse acting on a small area which is primarily due to high velocity of bullet.

In case of stone the velocity is low and size is large compared to bullet. So it fails to develop sufficient shear stress to punch the glass. So entire impulse causes bending of the glass which causes a tensile stress on the body. Glass is very weak in tension and it breaks along the radial lines due to this .

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

I think IIT committee is going to raise the eligibility limit for JEE from 60% to 85%. They are not going to count 12th mark for preparing JEE rank. I welcome this suggestion. Present 60% limit is too low for a reputed institute like IIT. I feel that they should initially raise this to 75 and see the effect.

 This Post 0 points    (0    in 0 votes )   [?]
Nothing wrong in raising the eligibility criterion from 60% to 85%. But the marks of 12th should not be counted for fixing the ranks because unifying various boards marks will be very difficult. Hope they don't go for a fifty-fifty formula. Some state boards are giving marks very generously!!!
 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

1) In case of train accelerating tension  in the string will be more compared to the tension in the case of train traveling in an incline. May be this can be found by tapping the string with your finger.

2) Since the restoring acceleration is more in case of train traveling with acceleration(root(g^2+a^2)) the period of oscillation will be less here compared to incline case.

But you have to make an observation when the train is stationary in advance so that you can differentiate between two cases!

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

Is it not the other way round? When water flow rate increases in a pipe we will be pushed backward. I think it is because of recoiling effect. Similar to bullets going out of a gun.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

760 mm Hg column = 10,000 mm of Water column(approx.)

By reducing pressure at lungs to 750 mm a differential pressure of 10 mm is created. This amounts to (10000/760)*10 = 131.5 mm of water column. So the length of straw has to be less than this.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

It makes a difference in weight only if we use a spring balance. If common balance is used there will be no difference in indicated mass as effects of variation in  'g' gets cancelled. For measuring 500 kg of sugar one must be using platform balance where again change  in 'g' doesn't matter.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

Dear all,

I wish all the best to evryone appearing for tomorrow's JEE!

Pls give the feedback after the test.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

In FPS system, pound(lb) is the unit of force, is n'i it?

In that case ft-lb/s is the unit of power. I am afraid, forum experts comment is wrong.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

Logically yes, but what happens if velocity is negetive initially. By sign convention if we take downward direction as positive( stone thrown up case) and upward negetive we get positive acceleration causing a "decrease" in speed in above example.  But the velocity is not decreasing  because it is negetive. A negetive quantity is increasing when the magnitude decrease. That is why assertion uses the word "speed".

Doesn't +ve acceleration mean acceleration in the direction of velocity??

 Discussion Forums -> This Post 5 points    (1    in 1 votes )   [?]

Assertion is true.

Suppose the velocity and acceleration are in opposite direction initially. Then velocity will come down for some time and there after it starts increasing. Eg: A stone thrown up . Here if we take donward direction as positive acceleration is positive and velocity negetive.

Reason is also true. But not a correct explanation for the assertion.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

See  both vertical forces are collinear. So I think the distance between them may not matter. But as you said rightly there is no proof that they are  equal.  We are assuming that as suggested. In the real case the distribution of the vertical forces between the hinges depend on their individual stiffness, and dimensional equality. If there is slight eccentricity there will be diifference in force . I really appreciate your perseverance in solving this problem fully.

Best of luck! Goodnight!

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

Can the velocity of the string and the block be different? Then there will be a slip or break of string. I feel it has to be same as that of block for continuity of the act of pulling.

Ofcourse the tension in the string can be resolved. Horizontal component will help in pulling while vertical component may help in reducing friction. But velocity should remain same , I feel.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

A similar problem is given in HCV rotational Mechanics Xth chapter, 44th question. There ,it is twritten,if magnitudes of forces exerted by hinges on the door are equal find this magnitude.

You have no other way. You have to assume that vertical  forces are equal in magnitude. Horizontal forces are equal in magnitude from analysis.

 Discussion Forums -> This Post 0 points    (0    in 0 votes )   [?]

You see there are four unknowns here N1,N2,N3 and N4. We have only three equation. So we cannot solve all the reaction with this equations. I feel that it is an indeterminate problem!

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