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 energy : forms and sources concept of energy energy for everything forms of energy

An object of mass $40\ kg$ is raised to a height of $5\ m$ above ground. If the object is allowed to fall down find its kinetic energy when it is half-way down.

  1. 1960 J

  2. 980 J

  3. 990 J

  4. 1000 J
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Gravitational Potential energy, $W = mgh$

$h=$ vertical displacement $=5\ m$

$m =$ Mass of object $= 40\ Kg$

$g =$ Acceleration due to gravity $= 9.8\ ms^{-2}$

$W = 40 \times 5 \times 9.8= 1960\ J$

For half way down$=\dfrac{1960}{2}= 980\ J$

At this point i.e. half way object has an equal amount of potential and kinetic energy.

Multiple choice physics energy : forms and sources concept of energy energy for everything forms of energy

A certain household has consumed $250$ units of energy during a month. How much energy is this in joules?

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

$1$ unit of energy $=1\ kWh$

$1\ kwh=3.6 \times 10^{6}\ J$

Thus $250$ unit$=250 \times 3.6 \times 10^{6}\ J$$=9 \times 10^{8}\ J$

Multiple choice economics consumption and investment functions keynesian law of consumption and propensity to consume ex ante and ex post concept of consumption function, saving function and investment function

If MPC = 0.8 and fixed consumption is 600, write the consumption equation.

  1. C = 600 + 0.8Y

  2. C = 600 - 0.8Y

  3. C = 600 + 0.2Y

  4. C = 0.2 Y - 600
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The Keynesian consumption function is given as: C = a + b Y 

where, C= Consumption, 

Y = Income

a = autonomous consumption and 

b = marginal propensity to consume 

So C = 600 + 0.8 Y

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

If the heart pushes 1 cc of blood in one second under pressure of 20000$Nm^{-2}$, the power of heart is

  1. 0.02 W

  2. 400 W
  3. $5\times 10^{-10}W$

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

Given,

$P=20000Nm^{-2}$
$\dfrac{dV}{dt}=1cc/s$
Power, $P=\dfrac{W}{t}=F.v=PA\dfrac{dx}{dt}$   (as, $F=PA$)
$P=P.\dfrac{dV}{dt}$
$P=20\times 10^3\times \dfrac{1}{(10^2)^3}$
$P=\dfrac{2}{100}=0.02W$
The correct option is A.

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

A pump can hoist 9000 kg of coal per hour from a mine of 120 m deep. calculate the power of the pump, in watts, assuming its efficiency is 75%, g=9.8 $m/s^{2}$

  1. 3.92 watts

  2. 39.2 watts

  3. 392 watts

  4. 3920 watts
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Work = mgh = 9000 kg * 9.8 m/s^2 * 120 m = 10,584,000 J. Power = Work / time = 10,584,000 J / 3600 s = 2940 W. Given 75% efficiency, the required power input is 2940 / 0.75 = 3920 W.

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

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

  1. 100 litre

  2. 1000 litre

  3. 1200 litre

  4. 2000 litre
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Power = 4000 W. Time = 60 s. Work = Power * time = 240,000 J. Work = mgh -> 240,000 = m * 10 * 20 -> 240,000 = 200m -> m = 1200 kg. Since 1 kg of water = 1 liter, the volume is 1200 liters.

Multiple choice elements of accounts accounts from incomplete records stakeholders and their information requirements ascertainment of profit and loss calculation of profit or loss under single entry system of accounting and statement of affairs accounts from incomplete records - single entry system

If beginning work in process equivalent units are 2500 units, work done in current period equivalent units are 3800 units and ending work in process equivalent units are 5000, then complete equivalent units in current period are ____________.

  1. 1800 units

  2. 1600 units

  3. 1300 units

  4. 1500 units
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The equivalent units completed in the current period are calculated as: (Total units to account for) - (Beginning WIP) - (Ending WIP). However, using the standard formula for equivalent units: Current period units = (Total equivalent units) - (Beginning WIP equivalent units). Given the data, the calculation is 3800 - 2500 = 1300 units.

Multiple choice physics energy and its forms idea of energy introduction to work and energy work and energy

Number of kilowatt-hours = $\displaystyle \frac{volt \times ampere \times  \,...........}{1000}$

  1. time in seconds

  2. time in minutes

  3. time in hours

  4. time in days
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Power, $P=VI$

1 kilowatt-hour means $P=1 kW=1000 W$ and time $t=1 hour$
As kWh is the unit of electrical energy so $1 kWh=VIt/1000$. 
Thus, time will be in hour.