Tag: energy and its forms

Quizzes (9) Questions (123)

Questions Related to energy and its forms

Multiple choice power work and power work, energy and power physics 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) $.

  1. $50 W$
  2. $50\times 20W$
  3. $80 W$
  4. $50\times 20\times 2W$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

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

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

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

  1. Power increased

  2. Power decreased

  3. Energy increased

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

Since time is increased,power decreased.

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

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 $(\rho _{Hg} = 13.6\times 10^{3} kgm^{-3})(g = 9.8\ ms^{-2})$.

  1. $60.97\ W$
  2. $63.97\ W$
  3. $1.12\ W$
  4. $83.97\ W$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

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

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

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?

  1. $15\ KW$
  2. $30\ KW$
  3. $100\ KW$
  4. $300\ KW$
Reveal answer Fill a bubble to check yourself
D Correct answer
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.

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

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

  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. $mg\, \left [ \displaystyle \frac{gt}{4}\, - u sin \theta \right ]$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Average power of gravity = Work / time. Work done by gravity = -m * g * delta_y. Delta_y = u * sin(theta) * t - (1/2) * g * t^2. Work = -m * g * (u * sin(theta) * t - 0.5 * g * t^2). Power = Work / t = -m * g * (u * sin(theta) - 0.5 * g * t) = m * g * (0.5 * g * t - u * sin(theta)).

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

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

  1. 0.02 W

  2. 400 W
  3. $5\times 10^{-10}W$

  4. 0.2 W
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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 $m/s^{2}$

  1. 3.92 watts

  2. 39.2 watts

  3. 392 watts

  4. 3920 watts
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work = mgh = 9000 kg * 9.8 m/s^2 * 120 m = 10,584,000 J. Power = Work / time = 10,584,000 J / 3600 s = 2940 W. Given 75% efficiency, the required power input is 2940 / 0.75 = 3920 W.

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

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? 

  1. Zero

  2. Positive

  3. Negative

  4. Nothing can be said
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

If we consider work done against gravity, walking from one point to the antipodal point involves moving away from Earth's center then descending back down. The net work against gravity is zero (positive climbing cancels negative descending). However, the question is poorly specified as the person does positive muscular work throughout.

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

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 

  1. 100 litre

  2. 1000 litre

  3. 1200 litre

  4. 2000 litre
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Power = 4000 W. Time = 60 s. Work = Power * time = 240,000 J. Work = mgh -> 240,000 = m * 10 * 20 -> 240,000 = 200m -> m = 1200 kg. Since 1 kg of water = 1 liter, the volume is 1200 liters.

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

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

  1. 8 dyne

  2. 4 dyne

  3. 16 dyne

  4. 32 dyne
Reveal answer Fill a bubble to check yourself
D Correct answer
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.