Physics

Power, Energy, and Efficiency

443 Questions

Power, energy, and efficiency are fundamental physics concepts that quantify work and the rate of doing work. Questions cover electrical energy consumption in kilowatt hours, the efficiency of thermodynamic cycles like the Brayton cycle, and mechanical power lifting loads. This topic is essential for general science and engineering exam preparation.

Electrical energy consumptionBrayton cycle efficiencyPower calculation formulasCommercial electricity unitsHydraulic lift mechanics

Power, Energy, and Efficiency Questions

Multiple choice chemistry water in our life how can we conserve water? droughts, floods and water conservation conservation of water and its importance and methods

The efficiency of drip irrigation is around: 

  1. 40%

  2. 85%

  3. 20%

  4. 100%
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Drip irrigation is one of the most efficient methods of irrigation. It supplies one drop at a time through small emitters. Thus it does not have little water runoff and very less water is lost during spraying. Thus its efficiency ranges from $80$% to $90$%

Multiple choice physics work and energy law of conservation of energy the law of conservation of energy types of energy

If 0.5 of any substance is completely transformed into energy, then how much energy in kilo-joule will be obtained?

  1. $1.5\times 10^{10} kilo-joule$
  2. $3.0\times 10^{10} kilo-joule$
  3. $4.5\times 10^{10} kilo-joule$
  4. $6.0\times 10^{10} kilo-joule$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Using $E=mc^2$
$m=0.5 g=5\times 10^{-4}kg$
$c=3\times 10^5m/s$
Hence, $E=5\times 10^{-4}\times (3\times 10^8)^2J$
$45\times 10^{12}J$
$=4.5\times 10^{10}kJ$

Multiple choice botany sustainable development with equity sustainable management conservation sustainable development

Of all of the energy production in the United States, what percentage is lost in distribution and inefficient use?

  1. 10

  2. 25

  3. 40

  4. 50
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Energy loss in the United States occurs throughout the generation, transmission, and distribution process. Estimates often cite that approximately 40 percent of energy is lost due to inefficiencies in conversion and delivery.

Multiple choice physics a little effort, lot of work motion in application common machines introduction to simple machines

In an ideal mechanical the output energy is :

  1. more than input energy

  2. equal to input energy

  3. less than input energy

  4. infinite compared to input energy
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Ideal machine. The term ideal machine refers to a hypothetical mechanical system in which energy and power are not lost or dissipated through friction, deformation, wear, or other inefficiencies.The mechanical efficiency of a simple machine is calculated by dividing the actual power output by the ideal power output.

Multiple choice maths direct proportion and inverse proportion rule of three types of proportions direct proportion

If 18 pumps can raise 2170 tonnes of water in 10 days, working 7 hours a day then in how many days will 16 pumps raise 1736 tonnes of water, working 9 hours a day ?

  1. 6

  2. 7

  3. 8

  4. 9
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the required number of days be x.
 Then,

Less pumps, More days (Indirect Proportion)


Less water, Less days (Direct Proportion)


More hours / day, Less days (Indirect Proportion)
 Pumps 8 : 9


Weight 1085 : 868
 Hours/day 9 : 7 :: 10 : x
$ (8 \times  1085 \times  9 \times  x) = (9 \times  868 \times  7 \times  10)$
$ x = (9 \times  868 \times  7 \times  10)/(8 \times  1085 \times  9)$
$ x=7 $
Answer (B) 7

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

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

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.

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

A lamp rated 20w and an electric iron rated 50w are used for 2 hour everyday. Calculate the total energy consumed in 20 days.

  1. 14kwh

  2. 2.8kwh

  3. 40kwh

  4. All
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Energy consumed by lamp in 2 hour     $E _l = 0.02\times 2 = 0.04$ kWh per day

Energy consumed by iron in 2 hour     $E _i = 0.05\times 2 = 0.1$ kWh per day
$\therefore$ Total energy consumed by both appliance     $E _T = (E _l+E _i)\times 20 = (0.04+0.1)\times 20 = 2.8$ kWh