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 physics sound: production of sound oscillation - amplitude, time period and frequency of oscillation time period, frequency and amplitude of sound oscillatory and periodic motion

The piston in a petrol engine goes up and down 3000 times per minute. For this engine, calculate the period of the piston.

  1. 0.02 s

  2. 0.04 s

  3. 0.05 s

  4. 0.08 s
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The frequency (f) of a wave is the number of full wave forms generated per second. This is the same as the number of repetitions per second or the number of oscillations per second.  
Time Period (T) is the number of seconds per waveform, or the number of seconds per oscillation.  It is clear that frequency and period are reciprocals. 
In this case, The piston in a petrol engine goes up and down 3000 times per minute, that is, 60 seconds. 
That is, the frequency is given as $f=\frac { 3000 }{ 60 } =50Hz$.
Time period = $\frac { 1 }{ f } =\frac { 1 }{ 50 } =0.02s$
Hence, the frequency is 50 Hz and the time period is 0.02 seconds.

Multiple choice chemistry substances in the surroundings - their states and properties measurement of density properties of substances fundamental and derived units

The heart of man pumps 5 litre of blood through the arteries per minute at a pressure of 150 mm of mercury. If the density of mercury. If the density of mercury be $13.6 \times 10^3 \ kg/m^3$ and g = 10 m/$s^2$ then the power of heart in watt is: 

  1. $2.35$
  2. $3.0$
  3. $1.50$
  4. $1.70$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Power = Pressure × (Volume/Time). Pressure = ρgh = (13.6×10³ kg/m³)(10 m/s²)(0.150 m) = 20,400 Pa. Flow rate = 5 L/min = 5×10⁻³ m³/60 s = 8.33×10⁻⁵ m³/s. Power = (20,400)(8.33×10⁻⁵) = 1.70 W. Option D is correct.

Multiple choice bio-chemistry carbohydrate metabolism energy output living organisms and energy production respiration in cell

Usable energy available from respiration is

  1. 10%

  2. 30%

  3. 40%

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

One mole of glucose on complete oxidation to carbon dioxide and water produces about 690,000 calories. About 10,000 calories are needed to form the high energy phosphate bonds in one mole of ATP. 36 or 38 moles of ATP formed in respiration process will trap 360,000 or 380,000 calories. The remaining 330, 000 or 310,000 calories are lost as heat. Thus about 52% of the energy released from glucose is trapped in ATP. 

Thus, the correct answer is option D. 

Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

One milligram of matter is converted into energy. The energy released will be

  1. $9\times 10^{6} J$
  2. $9\times 10^{8}J$
  3. $9\times 10^{10}J$
  4. $9\times 10^{12}J$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here, $m = 1\ mg = 1\times 10^{-3} g $

             $= 1\times 10^{-6}kg$
According to Einstein mass-energy equivalence
                $E = mc^{2}$
where $c$ is the speed of light in vacuum
$\therefore E = (1\times 10^{-6} kg)(3\times 10^{8}ms^{-1})^{2}$
$ = 9\times 10^{10}J$.

Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

The conversion of 1 u of mass results in ________ eV of energy.

  1. $9.315 \times 10^6$
  2. $391.5 \times 10^6$
  3. $931.5 \times 10^6$
  4. $93.15 \times 10^6$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

According to Einstein's mass-energy equivalence principle, 1 atomic mass unit (u) is equivalent to approximately 931.5 MeV of energy. Since 1 MeV equals 10^6 eV, 931.5 MeV equals 931.5 * 10^6 eV.

Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

One milligram of matter convert into energy will give

  1. $90 joule$
  2. $9\times { 10 }^{ 3} joule$
  3. $9\times { 10 }^{ 5} joule$
  4. $9\times { 10 }^{ 10} joule$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$E={ mc }^{ 2 }={ 10 }^{ -3 }\times{ 10 }^{ -3 } \left( 3\times { 10 }^{ 8 } \right) ^{ 2 }=9\times { 10 }^{ 10 }J$

Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

1mg of matter convert into energy will give

  1. $90$ joule
  2. $9\times { 10 }^{ 3 }$ joule
  3. $9\times { 10 }^{ 5 }$ joule
  4. $9\times { 10 }^{ 10 }$ joule
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$E=m{ c }^{ 2 }=10^{ -3 }\times { 10 }^{ -3 }\times { \left( 3\times { 10 }^{ 8 } \right)  }^{ 2 }= 9\times { 10 }^{ 10 }J$

Multiple choice chemistry matter around us measurement of properties effect of temperature and pressure on states of matter general introduction: importance and scope of chemistry

Energy spent in kilowatt-hour $=\cfrac {volt \times...........\times......}{1000}$.

  1. ampere, hour

  2. ohm,min

  3. ampere,min

  4. joule,hour
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Energy = Work done $(in\ Watt) =  Power\times time = Voltage \times current \times time$


$Work\ done\ (in\ kilowatt) = \dfrac{(Voltage\times current\times time)}{ 1000}$

$Or\ work\ done\ (in\ kilowatt) = \dfrac{(Volt\times ampere\times hour)}{ 1000}$

Multiple choice economics environment and sustainable development need for sustainable development environmental economics sustainable development

At present, nearly ____________$\%$ of the energy consumed is obtained from Non-Commercial Traditional Sources.

  1. $45$
  2. $51$
  3. $23$
  4. $10$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Statistical data on energy consumption in India historically indicates that traditional sources account for approximately 23 percent of total energy consumption.