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Physics >> Mechanics Part 2 >> Fluid in motion Medical Exam

THE  TERMINAL SPEED ATTAINED BY AN Al  SPERE OF RADIUS 1mm  FALLING THROUGH H2O AT 200C WILL BE CLOSE TO ??

ANS 4.6 m/s

(assume laminar flow , specific gravity of Al=2.7 & η H2O =8X 10-4 PL.)

Asked By: SARIKA SHARMA
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Joshi sir comment

v = 2r2g(D-d)/9η

so v = 2(.001)2*9.8(2700-1000)/9*8*10-5

solve it 

Physics >> Electricity >> Capacitors IIT JEE
One end of a 10cm long silk thread is fixed to a large vertical surface of a charged nonconducting plate having a mass 10g and a charge of 4*10^-6 c . In equlibrium the thread makes an angle of 60 deg. With he vertical.find the surface charge density on plate.
Asked By: GAURAV MAHATE
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Joshi sir comment

according to the diagram 

tanθ = qE/mg = q(σ/2ε0)/mg

solve this eq. for σ.

Remember that length of the thread is not applicable in the question.

Physics >> Electricity >> Current Electricity Others

 what is a short circuit?

 

Asked By: SWARNENDU MANNA
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Joshi sir comment

to connect - and + of the cell together

Physics >> Electricity >> Electric Field and Potential Medical Exam

IN THE SOLUTION GIVEN BY AMIT TO MY PREVIOUS QUERY , THE FORMULA USED IS E=kq/r ,SIR I WANT TO KNOW IS IT IS CORRECT , DON'T YOU THINK IT SHOULD BE E=kq/r2 ??

Asked By: SARIKA SHARMA
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Joshi sir comment

yes you are right

Physics >> Electricity >> Capacitors IIT JEE
there is slight mistake in last line of previous question.it was find the work done on the system in the process of inserting the slab.
Asked By: GAURAV MAHATE
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Joshi sir comment

 

initial energy of capacitor = 1/2 CV2

final energy of capacitor = 1/2 KC (V/K)2

difference ?

Physics >> Electricity >> Capacitors IIT JEE
a parallel plate capacitor of plate A and plate seperation d is charged to a potential dif. V and then the battery is disconnected .a slab of dielectric constant K is then inserted between the plates of capacitor so as tofill the space bet. The plates .find the work done in this process.
Asked By: GAURAV MAHATE
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Joshi sir comment

initial energy of capacitor = 1/2 CV2

final energy of capacitor = 1/2 KC (V/K)2

difference ?

Physics >> Electricity >> Electric Field and Potential IIT JEE

A point charge q is placed off centre at point c inside a thick spherical shelll of inner radius a and outer radius b. Shell is neutral and conducting. OA =ra , OB = rb & OC = rc. Then the potential at centre of shell will be ( also show the distribution of charges )

Asked By: AMIT DAS
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Joshi sir comment

Distribution:         at C q, at inner surface -q, at outer surface +q

so potential at centre = kq/rc -kq/a + kq/b

 

Physics >> Electricity >> Electric Field and Potential IIT JEE

A particle P of charge q and mass m is placed at a point in gravity free space and its free to move. another particle Q , of same charge and mass , is projected from a distance r from P with an initial speed v0  towards p . Initially the distance between P and Q decreases and then increases. Then what will be the speeds of particles P and Q when their separation is minimum?

Asked By: AMIT DAS
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Joshi sir comment

by momentum conservation mv0 = 2mv1

so v1 = v0/2 

Physics >> Electricity >> Electric Field and Potential IIT JEE
A charge q kept at the center of a semicircular thread having uniform charge per unit length lameda R is the radius of semivircular thread. Find the force req. ti keep it stationary ???
Asked By: SHUBHAM CHAUDHARY
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Joshi sir comment

first calculate the magnitude of electric field at centre of ring due to charge on the surface of ring and direction of that electric field also

this can be solved by method of integration 

then F = qE

if uncleared reply, we will give complete answer

Physics >> Mechanics part 1 >> Centre of mass and momentum conservation IIT JEE
a ball falls on an inclined plane of inclination @ from a height h above the point of impact and makes a perfectly elastic collisiom.where will it hit the plane again?
Asked By: GAURAV MAHATE
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Joshi sir comment

velocity of impact = √2gh

so components of velocity after rebound = √2ghcosθ perpendicular to the plane and √2ghsinθ parallel to the plane for the collision is perfectly elestic

now with perpendicular component take net displacement 0 and calculate time 

then find displacement along the plane by using s = ut + 1/2at2

here remember that you should divide gravity in comnents too

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