Tag: energy and its forms

Questions Related to energy and its forms

A girl of mass $40 kg$ climbs $50$ stairs each of average height $20 cm$ in $50 s$. Find the power of the girl $\left( g=10m{ s }^{ -2 } \right) $.

power work and power work, energy and power physics energy and its forms

  1. $50 W$

  2. $50\times 20W$

  3. $80 W$

  4. $50\times 20\times 2W$

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Correct Option: C
Explanation:

Power $=\dfrac{work \quad done}{time}$

$=\dfrac { change\quad in\quad PE }{ time } \ =\dfrac { 40\times 10\times 50\times 20\times { 10 }^{ -2 } }{ 50 } \ =80W$

In a factory, due to a sudden strike the work usually done in a day took a longer time. Which of the following happened?

power work and power work, energy and power physics energy and its forms

  1. Power increased

  2. Power decreased

  3. Energy increased

  4. None of these

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Correct Option: B
Explanation:

Power $=\dfrac{work \quad done}{time}$

Since time is increased,power decreased.

In each heart beat, a heart pumps $80\ ml$ of blood at an average pressure of $100\ mm$ of $Hg$. Assuming $60$ heart beats per second, the power output of the heart is $(\rho _{Hg} = 13.6\times 10^{3} kgm^{-3})(g = 9.8\ ms^{-2})$.

power work and power work, energy and power physics energy and its forms

  1. $60.97\ W$

  2. $63.97\ W$

  3. $1.12\ W$

  4. $83.97\ W$

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Correct Option: B
Explanation:

Power=$P\times\Delta V\times beat\ rate$

$\rho gh\Delta V\times 60$
$13.6\times10^3\times9.8\times 100\times 10^{-3}\times80\times10^{-6}\times60=63.97\ W$

An area of land is an average of $2\ m$ below sea level. To prevent flooding, pumps are used to lift rainwater up to sea level. What is the minimum pump output power required to deal with $1.3 \times 10^9\ Kg$ of rain per day?

power work and power work, energy and power physics energy and its forms

  1. $15\ KW$

  2. $30\ KW$

  3. $100\ KW$

  4. $300\ KW$

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Correct Option: D
Explanation:

Given,

$m=1.3\times 10^9 kg$
$g=10m/s^2$
$h=2m$
$t=1day$
Power, $P=\dfrac{mgh}{t}$
$P=\dfrac{1.3\times 10^9\times 10\times 2}{1\times 24\times 60\times 60}$
$P=300\times 10^3=300kW$
The correct option is D.

A stone is projected with velocity $u$ at an angle $\theta$ with horizontal. Find out average power of the gravity during time t.

power work and power work, energy and power physics energy and its forms

  1. $mg\, \left [ \displaystyle \frac{gt^2}{2}\, - u sin \theta \right ]$

  2. $mg\, \left [ \displaystyle \frac{gt}{2}\, + u sin \theta \right ]$

  3. $mg\, \left [ \displaystyle \frac{gt}{2}\, - u sin \theta \right ]$

  4. $mg\, \left [ \displaystyle \frac{gt}{4}\, - u sin \theta \right ]$

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Correct Option: C

If the heart pushes 1 cc of blood in one second under pressure of 20000$Nm^{-2}$, the power of heart is

power work and power energy and its forms work, energy and power physics

  1. 0.02 W

  2. 400 W

  3. $5\times 10^{-10}W$

  4. 0.2 W

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Correct Option: A
Explanation:

Given,

$P=20000Nm^{-2}$
$\dfrac{dV}{dt}=1cc/s$
Power, $P=\dfrac{W}{t}=F.v=PA\dfrac{dx}{dt}$   (as, $F=PA$)
$P=P.\dfrac{dV}{dt}$
$P=20\times 10^3\times \dfrac{1}{(10^2)^3}$
$P=\dfrac{2}{100}=0.02W$
The correct option is A.

A pump can hoist 9000 kg of coal per hour from a mine of 120 m deep. calculate the power of the pump, in watts, assuming its efficiency is 75%, g=9.8 $m/s^{2}$

power work and power energy and its forms work, energy and power physics

  1. 3.92 watts

  2. 39.2 watts

  3. 392 watts

  4. 3920 watts

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Correct Option: D

A man starts walking from a point on the surface of earth (assumed smooth) and reaches diagonally opposite point. What is the work done by him? 

power work and power energy and its forms work, energy and power physics

  1. Zero

  2. Positive

  3. Negative

  4. Nothing can be said

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Correct Option: A

The power of water pump is 4 kW. If g = 10 $ms^{-2}$, the amount of water it can raise in 1 minute to a height of 20 m is 

power work and power energy and its forms work, energy and power physics

  1. 100 litre

  2. 1000 litre

  3. 1200 litre

  4. 2000 litre

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Correct Option: C

The force acting on a 4gm mass in the energy region ${ U=8x }^{ 2 }$ at x= -2 cm is :

physics energy and its forms idea of energy introduction to work and energy work and energy

  1. 8 dyne

  2. 4 dyne

  3. 16 dyne

  4. 32 dyne

Show answer
Correct Option: D
Explanation:

Given,

$m=4gm$
$U=8x^2$

The force acting on mass $m$ in the potential energy $U$  at $x=-2cm$ will be

$F=-\dfrac{dU}{dx}$
$F=-\dfrac{d(8x^2)}{dx}$
$F=-16x$
$|F| _{x=-2cm}=-16\times(-2)=32dyne$
The correct option is D.