Tag: commercial unit of energy

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Questions Related to commercial unit of energy

Multiple choice physics work and power commercial unit of energy power work and energy

A two kilowatt motor pumps out water from a well 10 meter deep. The quantity of water pumped out per hour  is ( g = 10 $m/s^2$)

  1. $72 \times 10^2$ kg
  2. $72 \times 10^3$ kg
  3. $72 \times 10^4$ kg
  4. $72 \times 10^5$ kg
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Two kilowatt motor  pump means that 2kJ wotk is done in $1$ sec 

Let $m$ be the mass of water that is pumped out 
Work done , $W=2\ kJ=2000\ J$
Time taken , $t=1 sec$

Displacement of water , $h= 10\ m$

As in this case  $W=mgh $

$\implies 2000= m\times 10\times 10$
$\implies m=20\ kg$

Quantity of water pumped out per sec , $m=20\ kg$

$\therefore \text{ Quantity of water that is pumped out per hour }= m\times 3600=20\times 3600= 72\times 10^3 \ kg $

Multiple choice physics work and power commercial unit of energy power work and energy

If the heart pushes 1 cc of blood in one second under pressure 20000 $N/m^2$ the power of heart is:

  1. 0.02 W

  2. 400 W

  3. 20 mW

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

Given that , 
Pressure ,$P=2000 N/m^2$
Change in Volume = $1 cc= 10^{-6 } L $

$\text{Power}=\dfrac{\text{workdone}}{\text{time}}=\dfrac{\text{pressure }\times \text{ change in volume}}{\text{time}}=\dfrac {2000\times 10^{-6}}{1}= 0.02 \ W$

Multiple choice physics work and power commercial unit of energy power work and energy

The pump of a water pumping system uses $2.0\ kW$ of electrical power when raising water. The
pumping system lifts $16kg$ of water per second through a vertical height of $7.0\ m$.
What is the efficiency of the pumping system?

  1. $1.8\%$
  2. $5.6\%$
  3. $22\%$
  4. $55\%$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The power of pump = $\dfrac{d(mgh)}{dt}$

                                 = $(16 \times 10 \times 7 ) W$
                                  = $112 W$
So, efficiency = $\dfrac{P _{out}}{P _{in}}\times 100$
                       = $\dfrac{112}{2000} \times 100$
                       =  $5.6 %$%

Multiple choice physics work and energy commercial unit of energy power work and power

Choose the correct option.

  1. kW$=$ unit of power and kWh $=$ unit of energy.
  2. kW$=$ unit of energy and kWh $=$ unit of power.

  3. kW and kWh are both of unit of energy.

  4. kW and kWh are both of unit of power.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Electrical Power is measured in watts (W), kilo-watts (kW), mega-watts (MW), and giga-watts (GW). The power of a load can change quickly, especially if the load is turning on and off.

Electrical Energy is measured in kilowatt-hours (kWh), megawatt-hours, and sometimes (less commonly) in watt-hours or watt-seconds. Energy is the primary measurement used by the utility company to determine your bill each month (although demand and power factor are also sometimes used). Unlike power, energy does not change quickly, but instead accumulates gradually.

Multiple choice physics work and energy commercial unit of energy power work and power

In our household applications, commercial unit of electricity is used. One unit is equal to:

  1. $1\ kW$
  2. $1\ kWh$
  3. $1\ kW/h$
  4. $1\ Wh$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Electrical Energy is measured in kilowatt-hours (kWh). A unit is the primary measurement used by the utility company to determine your bill each month (although demand and power factor are also sometimes used). Unlike power, energy does not change quickly, but instead accumulates gradually.

Multiple choice physics work and power commercial unit of energy power work and energy

$250 kg$ of water per minute is to be drawn from a well $150 m$ deep. An electric pump of _______ can be used. $(g = 10 m/s^2) $ 

  1. 6 horse power

  2. 7 horse power

  3. 8 horse power

  4. 9 horse power
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Power, $P = \dfrac{w}{t} = \dfrac{mgh}{t} =\dfrac{mgh}{t\times 746} HP = 8.35HP$
$\therefore Power$  $= 9HP$ 

Multiple choice physics work and energy commercial unit of energy power work and power

Which of the following can be used to express energy? Symbols have their usual meanings for the units of physical quantities.
(i) Wh   (ii) VC    (iii) VAs$^2$  (iv)  A$^2\Omega$s

  1. (i) , (ii)

  2. (ii), (iii), (iv)

  3. (i), (ii), (iv)

  4. (i), (ii), (iii), (iv)
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using   $E = Pt$       $\implies$ Energy can be expressed in $Wh$

Using  $W = qV$     $\implies$ Energy can be expressed in $VC$
Using  $H = i^2Rt$  $\implies$ Energy can be expressed in $A^2\Omega s$
Whereas  Energy cannot be expressed by  $VAs^2$
Hence option C is correct.

Multiple choice physics work and energy commercial unit of energy power work and power

Electric energy supplied to homes is measured by

  1. voltmeter

  2. ammeter

  3. galvanometer

  4. kilowatt-hour meter
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The kilowatt hour (symbolized kW⋅h as per SI) is a composite unit of energy equivalent to one kilowatt (1 kW) of power sustained for one hour. One watt is equal to 1 J/s. One kilowatt hour is 3.6 MJoules, which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour.

Multiple choice physics work and energy commercial unit of energy power work and power

1 kilowatt-hour is the amount of .... by 1000 watt electric appliance when it operates for one hour.

  1. Power

  2. Voltage

  3. Electric energy

  4. None
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

1 kilowatt-hour is the amount of energy energy consumed by a 1000 watt electric appliance when it is operated for one hour.