### JEE Mains Previous Years Questions with Solutions

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1

### AIEEE 2002

At what temperature is the $r.m.s$ velocity of a hydrogen molecule equal to that of an oxygen molecule at ${47^ \circ }C?$
A
$80K$
B
$-73$ $K$
C
$3$ $K$
D
$20$ $K$

## Explanation

${v_{rms}} =$$\sqrt {{{RT} \over M}}$

For ${v_{rms}}$ to be equal ${{{T_{{H_2}}}} \over {{M_{{H_2}}}}} = {{{T_{{O_2}}}} \over {{M_{{O_2}}}}}$

Here ${M_{{H_2}}} = 2;\,\,{M_{{O_2}}} = 32;$

${T_{{O_2}}} = 47 + 273 = 320K$

$\therefore$ ${{{T_{{H_2}}}} \over 2} = {{320} \over {32}}$

$\Rightarrow {T_{{H_2}}} = 20K$
2

### AIEEE 2002

Even Carnot engine cannot give $100\%$ efficiency because we cannot
A
B
find ideal sources
C
reach absolute zero temperature
D
eliminate friction.

## Explanation

$\eta = 1 - {{{T_2}} \over {{T_1}}}$
For $\eta = 1$ or $100\%$, ${T_2} = 0K.$
The temperature of $0$ $K$ (absolute zero) can not be obtained.
3

### AIEEE 2002

Cooking gas containers are kept in a lorry moving with uniform speed. The temperature of the gas molecules inside will
A
increase
B
decrease
C
remain same
D
decrease for some, while increase for others

## Explanation

Since pressure and volume are not changing, so temperature remains same.
4

### AIEEE 2002

If mass-energy equivalence is taken into account, when water is cooled to form ice, the mass of water should
A
increase
B
remain unchanged
C
decrease
D
first increase then decrease

## Explanation

When water is cooled to form ice, energy is released from water in the form of heat. As energy is equivalent to mass therefore when water is cooled to ice, its mass decreases.