### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2004

MCQ (Single Correct Answer)
A radiation of energy $E$ falls normally on a perfectly reflecting surface. The momentum transferred to the surface is
A
$Ec$
B
$2E/c$
C
$E/c$
D
$E/{c^2}$

## Explanation

Momentum of photon $= {E \over c}$

Change in momentum $= {{2E} \over c}$

$=$ momentum transferred to the surface

(the photon will reflect with same magnitude of momentum in opposite direction)
2

### AIEEE 2004

MCQ (Single Correct Answer)
If two soap bubbles of different radii are connected by a tube
A
air flows from the smaller bubble to the bigger
B
air flows from bigger bubble to the smaller bubble till the sizes are interchanged
C
air flows from the bigger bubble to the smaller bubble till the sizes become equal
D
there is no flow of air.

## Explanation

Pressure inside the bubble, P $= {p_0} + {{4T} \over R}$

So $P \propto {1 \over R}$ where R is the radius of the bubble. It means pressure inside a smaller bubble is greater than the inside of a bigger bubble.

So when two bubbles are connected by a tube, air will flow from smaller bubble to bigger bubble and the size of bigger bubble will increase.
3

### AIEEE 2004

MCQ (Single Correct Answer)
Spherical balls of radius $R$ are falling in a viscous fluid of viscosity $\eta$ with a velocity $v.$ The retarding viscous force acting on the spherical ball is
A
inversely proportional to both radius $R$ and velocity $v$
B
directly proportional to both radius $R$ and velocity $v$
C
directly proportional to $R$ but inversely proportional to $v$
D
inversely proportional to $R,$ but directly proportional to velocity $v$

## Explanation

From Stoke's law,

viscous force acting on the ball falling into a viscous fluid

$F = 6\pi \eta Rv$

$\therefore$ $F \propto R$ and $F \propto v$

hence $F$ is directly proportional to radius & velocity.
4

### AIEEE 2004

MCQ (Single Correct Answer)
A wire fixed at the upper end stretches by length $l$ by applying a force $F.$ The work done in stretching is
A
$2Fl$
B
$Fl$
C
${F \over {2l}}$
D
${{Fl} \over 2}$

## Explanation

Work done by constant force in displacing the object by a distance $\ell$.

= Potential energy stored

$= {1 \over 2} \times$ Stress $\times$ Strain $\times$ Volume

$= {1 \over 2} \times {F \over A} \times {l \over L} \times AL$

$= {1 \over 2}Fl$

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NEET

Class 12