Tag: energy and its forms

Questions Related to energy and its forms

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

A body of mass $10kg$ is moving along positive $x-$axis with $5\ m/s$ at $t=0$ and is moving along negative $x-$axis with same speed at $t=10\ s$. Average power of the force acting on the body is:

  1. $Zero$
  2. $25\ W$
  3. $50\ W$
  4. $100\ W$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

since there is no acceleration 

there is no power
P=0

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

A light bulb has the rating 100 W, 220 V. If the supply voltage is 110 V, then power consumed by the bulb is

  1. 50 W

  2. 75 W

  3. 25 W

  4. 20 W

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
$P =\dfrac{ V^2}R$  

If $V = 220$ V we have

$100 W =\dfrac{ 220^2}R$

$R = \dfrac{220^2}{100} Ω = 484 Ω$. This is the resistance of the bulb.

When $V = 110$ V, power consumed $=\dfrac{V^2}R= \dfrac{110^2}{484} = 25$ W.

So, 25 W power is consumed when it is operated on 110 V.


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

A force $\vec {F}=(3\hat {i}+4\hat {j})N$ acts on $2kg$ movable object that moves from an initial position $\vec {r} _{1}=(-3\hat {i}-2\hat {j})m$ to a final position $\vec {r} _{1}=(5\hat {i}+4\hat {j})m$ in $6s$. The average power delivered by the force during the interval of $6s$ is equal to :

  1. $8\ watt$
  2. $\dfrac{50}{6}\ watt$
  3. $15\ watt$
  4. $\dfrac{50}{3}\ watt$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 

Given,

Force, $\vec {F}=(3\hat {i}+4\hat {j})N$

Displacement, $\vec{d}={{\vec{r}} _{2}}-{{\vec{r}} _{1}}=(5\hat{i}+4\hat{j})-(-3\hat{i}-2\hat{j})=\left( 8\hat{i}+6\hat{j} \right)\,m$

Work, $W=\vec{F}.\vec{d}=\left( 3\hat{i}+4\hat{j} \right)\left( 8\hat{i}+6\hat{j} \right)=48\,J$

Average power $P=\dfrac{W}{t}=\dfrac{48}{6}=8\,W$

Average power is $8\,W$ 

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

A weight lifter lifts $300\ kg$ from the ground to a height of $2$ meter in $3$ seconds. The average power generated by him is:-

  1. $5880\ watt$
  2. $4410\ watt$
  3. $2205\ watt$
  4. $1960\ watt$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work = m * g * h = 300 * 9.8 * 2 = 5880 J. Power = Work / time = 5880 / 3 = 1960 W.

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

Human heart pumps $70\ cc$ of blood at each beat against a pressure of $125\ mm$ of $Hg$. If the pulse frequency is $72$ per minute, the power of the heat is nearly.

  1. $1.2\ W$
  2. $1.4\ W$
  3. $1.6\ W$
  4. $1.8\ W$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pressure P = 125 mm Hg = 0.125 * 13600 * 9.8 = 16660 Pa. Volume V = 70 cc = 70 * 10^-6 m^3. Work per beat = P * V = 16660 * 70 * 10^-6 = 1.1662 J. Power = Work * frequency = 1.1662 * (72 / 60) = 1.399 W, which is approximately 1.4 W.

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

A force F acting on a body depends on its displacement $S$ as $F \propto S^{1/3}$. The power delivered by $F$ will depend on displacement as:

  1. $S^{2/3}$
  2. $S^{-5/3}$
  3. $S^{1/2}$
  4. $S^0$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Also work done = Force $\times$displacement

As given $F \ \alpha \ {S}^{1/3}$

$F=KS^{ 1/3 }$------(1) (where $K$= constant of proportionality)

Now Power= $\dfrac{F \times S}{time}$----(2)
Putting value of 1 in 2 we get 

$P= {\dfrac{KS^{\dfrac{2}{3}}}{t}}$

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

An engine of ine metric ton is going up an inclined plane, 1 in 2 at the rate of 36 kmph. If the coefficient of friction is $1/ \sqrt{3}$, the power of engine is 

  1. 9.8W

  2. 98W

  3. 980W

  4. 98kW

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Force required = mg * sin(theta) + mu * mg * cos(theta). Slope 1 in 2 means sin(theta) = 0.5, cos(theta) = sqrt(3)/2. Force = 1000 * 9.8 * (0.5 + (1/sqrt(3)) * (sqrt(3)/2)) = 1000 * 9.8 * (0.5 + 0.5) = 9800 N. Velocity = 36 kmph = 10 m/s. Power = F * v = 9800 * 10 = 98000 W = 98 kW.

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

A train of mass $6 \times 10^2$ metric tones is pulled by a locomotive. The speed of the train will be $36 \,kmhr^{}-1$. The locomotive pulls the train on the train on the level track, whose mass is $125$ metric tones. The force of friction acts on the locomotive and the train is $1 \times 10^1$ newton per metric tonne. Calculate the power of the locomotive.

  1. 72500

  2. 6000

  3. 5000

  4. 4000

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$m = 600$
$m\ell = 125$
$m \,net = 725$
$f = \dfrac{10}{tan}$
$t _{net} = 10 \times 125$

$V = 36 \,km/h = 36 \times \dfrac{5}{18} m/s$

$P = t _{net} \times V = 72500 \,W$

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

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

  1. $100$ litre
  2. $1000$ litre
  3. $1200$ litre
  4. $2000$ litre
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Given that,

Power, $P=4\,kW=4000\,W$

Height, $h=20\,m$

Time, $t=60\,\sec $

$ power=\dfrac{work}{time} $

$ 4000=\dfrac{mgh}{t} $

$ 4000=\dfrac{m\times 10\times 20}{60} $

$ m=1200\,Kg $

The pump can raise 1200 litre in one minute

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

An object of mass accelerates uniformly from rest to a speed $v _f$ in time $t _f$ Then the instantaneous power delivered to the object,as a function of time $t$ is -

  1. $mt\left(\dfrac{{v _f}^2}{t _f}\right)$
  2. $mt\dfrac{v _f}{t _f}$
  3. $\dfrac{1}{2}mt^2\left(\dfrac{v _f}{t _f}\right)^2$
  4. $\dfrac{1}{2}mt^2\left(\dfrac{v _f}{t _f}\right)$
Reveal answer Fill a bubble to check yourself
A Correct answer