Tag: physics

Quizzes (598) Questions (13441)

Questions Related to physics

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

A $0.25 kg$ book falls from a height of $1.00 m$, initially at rest. What is the AVERAGE power output of gravity on the book in this time period?

  1. $2.45 W$
  2. $5.43 W$
  3. $10.9 W$
  4. $24.1 W$

  5. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given :   $m = 0.25$ kg               $S =1.00$ m                    $u =0$ m/s                $a = g = 9.8m/s^2$

Using   $S = ut+\dfrac{1}{2}at^2$
$\therefore$    $1.00 = 0 + \dfrac{1}{2} \times 9.8t^2$                                     $\implies t = 0.45$ s
 Work done by gravity         $W = mgh  =0.25 \times 9.8 \times 1.00 = 2.45$  J
$\therefore$Output power  of gravity        $P = \dfrac{W}{t} = \dfrac{2.45}{0.45} = 5.43$  $W$

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

Find the power of a pump which takes $10 s$ to draw $100 kg$ of water from a tank situated at a height of $20 m$.

  1. $2\times { 10 }^{ 4 }W$
  2. $2\times { 10 }^{ 3 }W$
  3. $200 W$
  4. $1 kW$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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


             =  $\dfrac{mgh}{time}$

            =  $\dfrac{100 \ast 10 \ast 20}{10}$

             =  $\dfrac{20000}{10}$

               = 2000W  i.e  2 $\times$ 10$^{3}$W

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

A $40 N$ force accelerates a $20 kg$ mass through a distance of $16 m$. If there were no other forces acting on the mass and the mass started at rest, what was the average power output of the force?

  1. $0 W$
  2. $160 W$
  3. $226 W$
  4. $640 W$

  5. Cannot be determined from the information given
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given :  $F = 40$ N            $m = 20$ kg              $S = 16$ m               $u = 0$ m/s

Thus acceleration of the mass        $a = \dfrac{F}{m} = \dfrac{40}{20} =2$  $m/s^2$
Using    $S = ut + \dfrac{1}{2}at^2$
$\therefore$  $16 = 0 + \dfrac{1}{2} \times 2 t^2$                      $\implies t = 4$ s
Work done by the force     $W = FS = 40 \times 16  =640$ J
$\therefore$ Power output        $P = \dfrac{W}{t} = \dfrac{640}{4} = 160$  W

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

An engine of $4.9 kW$ power is used to pump water from a well which is $20 m$ deep. What quantity of water in kiloliters can it pump out in $30$ minutes?

  1. $45 kl$
  2. $75 kl$
  3. $25 kl$
  4. $90 kl$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Power$=\dfrac{work}{time}=\dfrac{mgh}{t}$

$=\dfrac{4.9\times 10^3\times 30\times 60}{9.8\times 20}=m$
$m=45kl$

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 image formation by lens image formation by lenses ray optics and optical instruments optics physics

If David is observing his image in plane mirror. The distance between the mirror and his image is 4 m. If he moves 1 m towards the mirror, then the distance between David and his image will be :

  1. 3 m

  2. 5 m

  3. 6 m

  4. 8 m
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Plane mirror produces erect image and is of same size and also at the same distance from the mirror as the object.

if he moves 1 m, distance of object from mirror= 3 m

distance of image from mirror= 3 m

distance between image and object =6 m.