Tag: alternative fuels and energy sources

Questions Related to alternative fuels and energy sources

Hydrogen is not used as a household fuel because:

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  1. it is highly combustible gas

  2. its transportation is difficult

  3. Is not easily available

  4. all of these are true

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Correct Option: D
Explanation:
Though hydrogen has the highest calorific value, it is not used as a household fuel because:
1. It is not easily available and this makes it costly too.
2. It is highly combustible.
3. Transportation is difficult.

An energy efficient device for producing light is:

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  1. CFL

  2. CNG

  3. LPG

  4. MCB

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Correct Option: A
Explanation:

Compact fluorescent light bulbs are used in place of incandescent bulb because they use about 1/7 of the power used by the incandescent bulb. Hence, they are highly efficient in saving electricity.

An electron and a proton are moving under the influence of mutual forces. In calculating the change in the kinetic energy of the system during motion, one ignores the magnetic force of one on another. This is because,

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  1. the two magnetic forces are equal and opposite, so they produce no net effect

  2. the magnetic forces do no work on each particle.

  3. the magnetic forces do equal and opposite (but non-zero) work on each particle

  4. the magenetic forces are necessarily negligible

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Correct Option: B
Explanation:
The electric and magnetic forces are defined via the Lorentz force on a charged particle

$F =q(E +v ×B )$
The magnetic force comes from the second term which defines it to be perpendicular to the velocity and therefore displacement $dr$ so it doesn't do any work.

A sealed container with negligible coefficient of volumetric expansion contains helium (a mono-atomic gas). When it is heated from 300 K to 600 K, the average KE of helium atoms is:

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  1. halved

  2. unchanged

  3. doubled

  4. increased by factor $\sqrt2$

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Correct Option: C
Explanation:

$the\quad avarage\quad KE\quad of\quad n\quad moles\quad of\quad gas\quad at\quad temp\quad T\quad is\quad \dfrac { 3 }{ 2 } nRT\ when\quad temp\quad is\quad doubled\quad \dfrac { 3 }{ 2 } nR(2T)=2\times \dfrac { 3 }{ 2 } nRT\ so\quad KE\quad doubles$

If a man speed up 1m/s his KE increases by 44% His original speed in m/s is 

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  1. 1

  2. 2

  3. 5

  4. 4

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Correct Option: C

A point in the object where entire mass of an object is said to be concentrated is:

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  1. Point of Buoyancy

  2. Centre of Mass

  3. Point of Pressure

  4. None of these

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Correct Option: B
Explanation:

A point where entire mass of the body is assumed to be concentrated is called center of mass. This point may or may be inside body or outside.


A ball of mass 50 g is thrown upwards. It rises to a maximum height of 100 m. At what height its kinetic energy will be reduced to 70%?

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  1. 30 m

  2. 40 m

  3. 60 m

  4. 70 m

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Correct Option: A
Explanation:

By work energy theorem,

$U _i+K _i=U _f+K _f$
$0+K _i=mgh+0$
$K _i=(50\times10^{-3})(10)(100)J$
$K _i=50J$ $-(i$)
Now, we have $K _f=\dfrac{70}{100}K _i$
By work energy theorem,
$0+K _i=mgh+\dfrac{70}{100}K _i$
$K _i-\dfrac{70}{100}K _i=(50\times10^{-3})(10)(h)$
$\dfrac{30}{100}K _i=0.5h$
From $(i)$, we have $K _i=50$
$h=2\times\dfrac{30}{100}\times50m$
$h=30m$

The kinetic energy K of a particle moving along a circle of radius R depends on the distance s as $ K=as^2$. The force acting on the particle is 

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  1. $\dfrac{2 as^2}{R}$

  2. $2a[1+\dfrac{s^2}{R^2}]^{1/2}$

  3. $2as$

  4. $2a[\dfrac{R^2}{s}]^{1/2}$

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Correct Option: A

The total energy of an electron is 3.555 MeV then its kinetic energy is

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  1. $3.545 \mathrm { MeV }$

  2. $3.045 \mathrm { MeV }$

  3. $3.5 \mathrm { MeV }$

  4. none

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Correct Option: B
Explanation:

Every substance has energy due to its mass$:$

loss in energy
$\Delta E = \Delta m{c^2}$
$\therefore KE = \left( {m - {m _0}} \right){c^2}$
$ = 3.555 - {m _0}{c^2}$
$ = 3.555 - 0.51$
$ = 3.045MeV$
Hence,
option $(B)$ is correct answer.

A steady beam of alpha-particles $(p=2e)$ traveling with constant kinetic energy $20$ $MeV$ carries a current $0.251$ x $10^{-6}$. If the beam is directed perpendicular to a plane surface, how many alpha-particles strike the surface in $3$ secs? 

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  1. $2.3$ x $10^{12}$

  2. $2.3$ x $10^{19}$

  3. $2.3$ x $10^{8}$

  4. $2.3$ x $10^{6}$

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Correct Option: C