## Pressure

a glass jar contains a liquid of density ‘d’ up to aheight ‘h’ at a place where acceleration due to gravity ‘g’. the atmospheric pressure is PA. a) What is the pressure at the free surface of the liquid? b) Write an expression for the total pressure at the bottom of the jar . c) What will be the lateral pressure at this depth on the inner side of the jar?

Asked Jenny

## JEE 2013 emerges in its final form

The Joint Advanced Board (JAB) has announced that the Advanced **JEE**, scheduled to be conducted on June 2, 2013, will not be subjective and will retain **IIT JEE 2012** format. The test will be conducted in two sessions on the same day – each with objective-type multiple choice questions (MCQs). The difficulty level and marks allotted to Advanced JEE exam will also be similar to previous JEEs.

**IIT aspirants get another chance at Boards **

HRD ministry has allowed IIT aspirants a chance to appear for board exams again next year and improve their board marks. Hence, these students will get a chance to appear for JEE once again. The Central Board of Secondary Education (CBSE) and the state boards would make special arrangements to implement the decision.

**Only 10% IITians are girls**

Analyzing patterns of the Joint Entrance Examination (JEE) results 2012, the Joint Admission Board found that out of all the students admitted to 15 IITs, only 10% were girls. In other engineering institutes, including prestigious ones, the gender ratio is more balanced as 30-40 per cent girls got accepted.

## Kinematics Problem

Three particles A,B,C are situated at vertices of a equilateral triangle ABC of side ‘a’ m at t=0 Each of the particle moves with constant speed ‘ v ‘. A always has it’s velocity along AB ,B always has it’s velocity along BC , C always has it’s velocity along CA. Derive the equation of trajectory of any one particle (means find y=f(x) i.e. relation between y and x coordinates of the particle). Also find the rate of rotation of the triangle formed by joining the lines connecting the three points as a function of time. If you think it requires more information such as acceleration etc., introduce them if needed.

Asked uppinder

## Kinematics Problem

Three particles A,B,C are situated at vertices of a equilateral triangle ABC of side ‘a’ m at t=0 Each of the particle moves with constant speed ‘ v ‘. A always has it’s velocity along AB ,B always has it’s velocity along BC , C always has it’s velocity along CA. Derive the equation of trajectory of any one particle (means find y=f(x) i.e. relation between y and x coordinates of the particle). Also find the rate of rotation of the triangle formed by joining the lines connecting the three points as a function of time. If you think it requires more information such as acceleration etc., introduce them if needed.

Asked uppinder

## Light Amplification

If you passed directional light from a device such as a laser through the back of a 2 way mirror at a 45 degree angle and then directed that beam to 3 highly reflective mirrors at 45 degree angles in series so that the beam was directed back to the exact point it emerges from the two way mirror and creates an infinate loop what would happen? Would the beam change color since the particles would be out of sync because of the time delay? Would the light and heat of the beam amplify itself if the reflective surfaces were reflecting more than 50% of all the light emitted and more than 50% of the original sources light were transferred through the 2 way mirror? I included a drawing to simpilify the questions.

Asked Jeff

## Physics Numerical

If a stone is dropped from the edge of roof and passes by a window of height 2m in 0.1 second. Calculate the height of roof above the window. Show with process.

###### Related articles

- Physics Numerical Problems posted by Nabeela (askphysics.com)
- Numerical Problems from Kinematics (askphysics.com)

## Vibratory motion and periodic motion

**Say True or false**

Every motion made by a vibratory object and then back to its start point is a periodic motion

Note:

In this question its not mentioned that the motion is made in equal intervals of time. Please answer the question and justify it ?!

Posted by Khaled

Answer:

Vibratory motion caused by a restoring force acting on it when disturbed from mean position and inertia is essentially periodic.

Without a restoring force, the to an fro motion may not be periodic.