Tag: option b: engineering physics

Questions Related to option b: engineering physics

A heat engine is supplied with 250 kJ/s of heat at a constant fixed temperature of $227^0C$; the heat is rejected at $27^0C$, the cycle is reversible, then what amount of heat is rejected?

physics option b: engineering physics conversion of heat into work: heat engine and it's efficiency engines and cycles refrigerators and heat pumps

  1. 24kJ/s

  2. 223kJ/s

  3. 150kJ/s

  4. none of the above

Show answer
Correct Option: C
Explanation:

The temperature in kelvin scales are $T _1=273+27=300K,T _2=273+237=500K$

$T _1$is temperature of sink And$T _2$ is temperature of source hence by efficiency we get

$\eta=1-\dfrac{T _1}{T _2}=1-\dfrac{Q _1}{Q _2}$


$Q _1=\dfrac{T _1}{T _2}*Q _2=\dfrac{300}{500}*250=150kW$

An engine working on Carnot cycle rejects 40% of absorbed heat from the source, while the sink temperature is maintained at $27^0C$, then what is the source temperature (in $^0C$)?

physics option b: engineering physics conversion of heat into work: heat engine and it's efficiency engines and cycles refrigerators and heat pumps

  1. 477

  2. 346

  3. 564

  4. none of the above

Show answer
Correct Option: A
Explanation:
$\eta =\dfrac { 60 }{ 100 } $

${ T } _{ 2 }={ 27 }^{ o }C$
${ T } _{ 2 }={ 300 }^{ o }K$
${ T } _{ 1 }=?$

$\eta =\dfrac { { T } _{ 1 }-{ T } _{ 2 } }{ { T } _{ 1 } } $

Here, ${ T } _{ 1 }=Source\quad temperature$
${ T } _{ 2 }=sink\quad temperature$
$\eta =Efficiency$
$\eta =100-rejecion$

$\therefore \dfrac { 60 }{ 100 } =\dfrac { { T } _{ 1 }-{ T } _{ 2 } }{ { T } _{ 1 } } $

$\therefore 0.6=\dfrac { { T } _{ 1 }-300 }{ { T } _{ 1 } } $

$\therefore { T } _{ 1 }\left( 1-0.6 \right) =300$

${ T } _{ 1 }=\dfrac { 300 }{ 0.4 } =\dfrac { 3000 }{ 4 } ={ 750 }^{ o }K$

$\therefore { T } _{ 1 }={ \left( 750-273 \right)  }^{ o }C$
$\therefore { T } _{ 1 }={ 477 }^{ o }C$

One reversible heat engine operates between 1600 K and $T _2$ K, and another reversible heat engine operates between $T _2$ K and 400 K. If both the engines have the same heat input and output, then the temperature $T _2$ must be equal to:

physics option b: engineering physics conversion of heat into work: heat engine and it's efficiency engines and cycles refrigerators and heat pumps

  1. 600

  2. 800

  3. 650

  4. 675

Show answer
Correct Option: B
Explanation:

${ T } _{ 1 }=1600K$


${ T } _{ 2 }={ T } _{ 2 }K$


${ T } _{ 1 }^{ 1 }={ T } _{ 2 }K$

${ T } _{ 2 }^{ 1 }=400K$

Same input and same output.Then the efficiency is same.
$\eta =\dfrac { { T } _{ 1 }-{ T } _{ 2 } }{ { T } _{ 1 } } $

$\therefore \dfrac { 1600-{ T } _{ 2 } }{ 1600 } =\dfrac { { T } _{ 2 }-400 }{ { T } _{ 2 } } $

$=1600{ T } _{ 2 }-{ T } _{ 2 }^{ 2 }=1600{ T } _{ 2 }-640000$

$\therefore { T } _{ 2 }^{ 2 }=640000$
$\therefore { T } _{ 2 }=800K$

The freezer in a refrigerator is located at the top section so that;

physics option b: engineering physics conversion of heat into work: heat engine and it's efficiency engines and cycles refrigerators and heat pumps

  1. The entire chamber of the refrigerator is cooled quickly due to convection

  2. The motor is not heated

  3. The heat gained from the environment is high

  4. The heat gained from the environment is low

Show answer
Correct Option: A
Explanation:

The freezer in a refrigerator is located at the top section so that the entire chamber of the refrigerator is cooled quickly due to convection.  
The correct option is A.

If the door of a refrigerator is kept open, the room in which the refrigerator is kept 

physics option b: engineering physics conversion of heat into work: heat engine and it's efficiency engines and cycles refrigerators and heat pumps

  1. gets cooled

  2. gets heated

  3. neither gets cooled nor gets heated

  4. gets cooled or heated depending on the initial temperature of the room

Show answer
Correct Option: C

Consider the following statements:
(a)  Change in momentum is impulse.
(b)  A body is momentarily at rest when it reverse the direction.
(c)  For stable equilibrium force has to be zero and potential energy should be minimum.
(d)  Force required to accelerate a mass in two perpendicular directions is never same.
Which of the above statements are correct?

rotational equilibrium option b: engineering physics motion of system of particles and rigid bodies equilibrium physics

  1. (b) and (c)

  2. (a) and (b)

  3. (a), (b) and (d)

  4. All of the above

Show answer
Correct Option: D
Explanation:

All of the above
Impulse = Force$\times$time = $m\Delta{v}$ = Momentum
A body will be at rest for a moment when it changes direction.
When a body is in equilibrium it always has minimum potential energy and no force is acting upon it.
Force is a vector quantity and hence its direction will result in different force quantity.

State whether given statement is True or False.

When any object is in equilibrium, the sum of all the forces acting on it is zero.

rotational equilibrium option b: engineering physics motion of system of particles and rigid bodies equilibrium physics

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

When an object is not in equilibrium, net force acting on the body is not zero.
Therefore when some force acts on the object, it is in accelerated motion because, $F= ma$

Potential energy function $U(r)$ corresponding to the central force $F=K/r^{2}$ would be

rotational equilibrium option b: engineering physics motion of system of particles and rigid bodies equilibrium physics

  1. $-K/r$

  2. $-2K/r$

  3. $-r/K$

  4. $None of these$

Show answer
Correct Option: A
Explanation:
We know that as per definition of potential energy ( Only defined for conservative froces) ,
$U=\int -Fdr=-\dfrac{k}{r}$

When a body remains in the state of rest conditions under the influence of applied forces, the body is in 

rotational equilibrium option b: engineering physics motion of system of particles and rigid bodies equilibrium physics

  1. Dynamic equilibrium

  2. Static equilibrium

  3. Both

  4. None

Show answer
Correct Option: B
Explanation:

The equilibrium is of two types
(1) Static equilibrium
(2) Dynamic equilibrium
When a body remains in the state of rest under the influence of the applied forces, the body is in static equilibrium.

A body is in translatory equilibrium if:

rotational equilibrium option b: engineering physics motion of system of particles and rigid bodies equilibrium physics

  1. Resultant force on it is zero

  2. It is at rest

  3. It is in uniform motion

  4. All options are correct

Show answer
Correct Option: D
Explanation:

A body is said to be in translatory equilibrium when net external force acting on it is zero.

Also if no external force is acting on the body, then the body must be at rest or moving with constant velocity i.e moves in uniform motion. Hence option D is correct.