Tag: physics

Questions Related to physics

By sucking through a straw, a student can reduce the pressure in his lungs to $750 mm$ of Hg (density = $\displaystyle 13.6{ gm }/{ { cm }^{ 3 } }$). Using the straw, he can drink water from a glass upto a maximum depth of: 

physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

  1. $10 cm$

  2. $75 cm$

  3. $13.6 cm$

  4. $1.36 cm$

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Correct Option: C
Explanation:

Pressure difference created $= 10 mm$ of Hg 
This must be equal to the pressure of water column being created in the straw. If height of water column be $h$

$h \rho g = \dfrac{10}{10} \times 13.6 g$
$hg \times 1 = 13.6 g$
$h = 13.6 cm$

$1$ millibar is equal to a pressure of

physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

  1. ${10}^{5}pa$

  2. $100pa$

  3. $1000pa$

  4. ${10}^{-3}pa$

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Correct Option: B
Explanation:

We know that $1$ bar $= 10^5 Pa$

So, $1$ millibar $=10^{-3}$ bar $=10^{-3}\times 10^5 Pa=100 Pa$

One gram mole of oxygen is enclosed in a vessel at a temperature of $27$ and at one atmospheric pressure. The vessel is thermally insulated and is moved with a constant speed $u _0$. Calculate $u _0$ if the rise in temperature is $1K$ when the vessel is suddenly stopped?

physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

  1. $35.6 m/s$

  2. $45 m/s$

  3. $90 m/s$

  4. $60 m/s$

Show answer
Correct Option: B
Explanation:

since internal energy depends only on the temperature ,

as the temperature changes,
the change in internal energy is
$\Delta U= \dfrac{nfR \Delta T}{2}$

vessel contains a gas of mass M,
change in kinetic energy $= \dfrac{nMv^2}{2}$

$\dfrac{nfR \Delta T}{2}$= $\dfrac{nMv^2}{2}$

$\dfrac{2}{\dfrac{c _p}{c _v} - 1}$

$f = \dfrac{2}{\dfrac{2}{5}}$ = 5

putting value

$v = 45 m/s$

What will be the pressure in pascal due to a mercury column of $76$cm. Density of mercury is $13.6$ g$cm^2$, $g=980$ cm$s^2$?

physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

  1. $1.0129\times 10^5$Pa

  2. $1.0129\times 10^4$Pa

  3. $1.0129\times 10^3$Pa

  4. $1.0129\times 10^2$Pa

Show answer
Correct Option: A
Explanation:

 h$=76cm$

Pressure=?

Formula to be used : $P=hgd$

Where h = height of mercury column and

 d= density of mercury$=13.6 gm/cc$

acceleration due to gravity$=980 cm/s²$

$P=hgd=13.6\times 980\times 76=1012928dyne.cm²$

The height of the mercury column in a simple barometer is $h$. As the tube is inclined with the vertical at an angle $\alpha$, the length of the mercury column along the length of the tube will become:

physics fluid pressure pressure in air introduction to atmospheric pressure pressure exerted by air devices to measure pressure

  1. $h\cos{\alpha}$

  2. $\dfrac{h}{\cos{\alpha}}$

  3. $h\sin{\alpha}$

  4. $\dfrac{h}{\sin{\alpha}}$

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Correct Option: B

Graphite powder is used in machines to_______

physics common machines terms related to machines introduction to simple machines introduction to machines

  1. enhance friction

  2. enhance profit

  3. reduce friction

  4. reduce efficient

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Correct Option: C
Explanation:

Graphite powder is used in some machines to reduce friction. Ball bearing coverts sliding friction into rolling friction.

When the height of the inclined plane decreases :

physics simple machine common machines terms related to machines introduction to simple machines

  1. The mechanical advantage decreases

  2. The mechanical advantage increases

  3. Effort increases

  4. It will not have any effect on the mechanical advantage

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Correct Option: B
Explanation:

The mechanical advantage increases with decrease in height of inclined plane.

When the height of the inclined plane decreases :

physics simple machine common machines terms related to machines introduction to simple machines

  1. the mechanical advantage decreases

  2. the mechanical advantage increases

  3. effort increases

  4. it will not have any effect on the mechanical advantage

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Correct Option: B

For an ideal machine:

physics simple machine common machines terms related to machines introduction to simple machines

  1. Output= input

  2. Output> input

  3. Output< input

  4. Output ${\geq}$ input

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Correct Option: A
Explanation:

In an ideal machine there will be zero energy loss hence output will be equal to input

Mechanical advantage of a lever is

physics simple machine common machines terms related to machines introduction to simple machines

  1. load + effort

  2. load $\times$ effort

  3. $ \dfrac{load}{effort}$

  4. $ \dfrac{effort}{load}$

Show answer
Correct Option: D