Physics

Power, Energy, and Efficiency

463 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 spectra the electromagnetic spectrum electromagnetic spectrum electromagnetic waves

The sun delivers $10^3\, Wm^{-2}$ of electromagnetic flux on the earth's surface. The total power that is incident on a roof of dimensions $6 \,m \times 30\, m$ is 

  1. $1.8 \times 10^5\, W$
  2. $7.2 \times 10^5\, W$
  3. $0.9 \times 10^5\, W$
  4. $4.5 \times 10^5\, W$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Given, electromagnetic flux $=10^3\, Wm^{-2}$
The area of roof $A= 6\, m \times 30\, m$
$=180 \, m^2$
The total power incident on roof
$P=10^3 \times 180$
$=1.8\times 10^5 \, W$

Multiple choice physics simple machine common machines terms related to machines introduction to simple machines

Efficiency of machine is

  1. Ratio of velocity of effort to velocity of load

  2. Ratio of the load to its effort

  3. Ratio of useful work done by the machine to the work put to the machine by its effort

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

Mechanical advantage (MA) is the ratio of the load to its effort.
efficiency of machine (n) = MA/VR
Velocity Ratio (VR) is the ratio of the velocity of effort to velocity of load.

Multiple choice physics simple machine common machines terms related to machines introduction to simple machines

Efficiency is

  1. $\displaystyle \frac { Energy\quad input }{ Energy\quad output } \times 100$
  2. $\displaystyle \frac { mechanical\quad advantage }{ velocity\quad ratio } \times 100$

  3. Both

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

As no machine is perfectly efficient.
So, we define efficiency as efficiency = $\displaystyle \frac { Energy\quad input }{ Energy\quad output } \times 100$
Also Efficiency = $\displaystyle \frac { mechanical\quad advantage }{ velocity\quad ratio } \times 100$
A petrol engine is about 30% efficient, a diesel engine is 40% efficient.

Multiple choice physics simple machine common machines terms related to machines introduction to simple machines

The ratio of the work output to the work input of a machine is

  1. mechanical advantage

  2. efficiency

  3. work

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

Efficiency is the (often measurable) ability to avoid wasting materials, energy, efforts, money, and time in doing something or in producing a desired result. In a more general sense, it is the ability to do things well, successfully, and without waste. In more mathematical or scientific terms, it is a measure of the extent to which input is well used for an intended task or function (output).

Multiple choice physics simple machine common machines terms related to machines introduction to simple machines

The mechanical advantage of each machine is determined by

  1. adding the mechanical advantage for each simple machine

  2. finding the simple machine with the largest mechanical advantage

  3. finding the average mechanical advantage for the simple machines

  4. multiplying the mechanical advantage for each simple machine
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The mechanical advantage of each machine is determined by  multiplying the mechanical advantage for each simple machine.
Option D is correct

Multiple choice physics simple machine common machines terms related to machines introduction to simple machines

In a lifting machine, the efforts required for lifting loads of $20$ N and $30$ N were $5$ N and $6$ N respectively. If the velocity ratio of the machine is $20$, determine efficiencies corresponding to loads of $20 $ N and $30$ N

  1. 25 % and 20%

  2. 35% and 55%

  3. 30% and 50%

  4. 60% and 65%
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Let us take first case,


 in which $load=20N , effort =5N ,VR=20$

$Efficiency=\dfrac{load}{VR*effort}*100$

Putting above values, we get

$Efficiency=\dfrac{20}{20*5}*100=20%$

In second case we have.  $load=30N , efoort =6N ,VR=20$

$Efficiency=\dfrac{load}{VR*effort}*100$

Putting values we get,

$Efficiency=\dfrac{30}{20*6}*100=25%$

Hence$ Efficiency=25%,20%$

Multiple choice physics simple machine common machines terms related to machines introduction to simple machines

Efficiency of a machine can also be written as 

  1. $\dfrac{\text{velocity ratio}}{\text{mechanical advantage}} \times 100 $ %
  2. $\dfrac{\text{mechanical advantage}}{\text{velocity ratio}} \times 100 $ %
  3. $\dfrac{\text{mechanical advantage}}{\text{velocity of the gear}} \times 100 $ %

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

$effiency=\eta=\dfrac{Machanical-advantage}{velocity-ratio}*100$

Multiple choice physics lever common machines terms related to machines introduction to simple machines

An effort of 20 kgf is applied on a machine through a distance of 80 cm, when a load of 30 kgf moves through a distance of 1 cm. Calculate the velocity ratio of the machine.

  1. 40

  2. 80

  3. 160

  4. 60
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Velocity ratio $= \displaystyle \frac{distance \ of \ the \ effort}{distance \ moved \ by \ the \ load}$
$= \displaystyle \frac{80  cm}{1  cm}= 80$

Multiple choice physics lever common machines terms related to machines introduction to simple machines

A water -pump driven by petrol raises water at a rate $ 0.5 m^3/min $ from a depth of 30 m. if the pump is 70% efficient, what power is developed by the engine?

  1. 1750W

  2. 2450W

  3. 3500W

  4. 7000W
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Work done per minute = mgh = (0.5 m^3 * 1000 kg/m^3) * 10 m/s^2 * 30 m = 150,000 J. Power output = 150,000 J / 60 s = 2500 W. Power input = Output / Efficiency = 2500 / 0.7 = 3571 W. 3500 W is the closest answer.