Tag: energy transformations and energy transfers

Questions Related to energy transformations and energy transfers

In the foregoing question, the amount of energy given to the system from A to B is:

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. 50J

  2. 60J

  3. 30J

  4. 10J

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Correct Option: A

The specific heat capacity of a metal at low temperautre (T) is given as $C _ { p } \left( k \sqrt { k } - 1 k g ^ { - 1 } \right) = 32 \left( \frac { T } { 400 } \right) ^ { 3 }$ A 100 gram vessel of this metal is to be cooled from $20 ^ { \circ } K$ to $4 ^ { \circ } \mathrm { K }$ by a special refrigerator operating at room temperature $\left( 27 ^ { \circ } \mathrm { C } \right) .$ The amount of work required to cool the vessel is:-

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. equal to 0.002$\mathrm { kJ }$

  2. greater than 0.148$\mathrm { kJ }$

  3. between 0.148$\mathrm { kJ }$ and 0.028$\mathrm { kJ }$

  4. less than 0.028$\mathrm { kJ }$

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Correct Option: A

An ideal gas heat engine operates in a Carnot's cycle between $227^{\circ}C$ and $127^{\circ}C$. It absorbs $6\times 10^{4} J$ at high temperature. The amount of heat converted into work is _____.

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $4.8\times 10^{4}J$

  2. $3.5\times 10^{4}J$

  3. $1.6\times 10^{4}J$

  4. $1.2\times 10^{4}J$

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Correct Option: D

Work done by 100 calorie of heat is __________.

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. 418.4 J

  2. 4.184 J

  3. 41.84 J

  4. None of these

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Correct Option: A
Explanation:
For an isothermal expansion of an ideal gas, the change in internal energy is zero.

According to the first law of thermodynamics, 

Change in internal energy U = Q-W = 0

So, all the heat energy is utilized to do work. 

Q = W

We know that, one calorie is equal to 4.184 J

Therefore, Work done by 100 calorie of heat in an isothermal expansion of any ideal gas will be 4.184 * 100 =  418.4 Joule


A person of weight 60 kg wants to loose 5 kg by going up and down 10m high stairs. Assume he burns twice as much fat while going up than going down. If 1 kg of fat is burnt on expending 7000 kcal. How many times must he go up and down to reduce his 7 kg weight? (Take $  g=10 \mathrm{ms}^{-2} )  $

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $ 1.8 \times 10^{3} $ times

  2. $ 2.4 \times 10^{3} $ times

  3. $ 1.7 \times 10^{3} $ times

  4. $ 2.1 \times 10^{3} $ times

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Correct Option: C
Explanation:
Energy used to go up $=mgh=60\times 10\times 10=6000\,J$

Energy used to come down $\dfrac{6000}{2}=3000\,J$

Energy used in one round trip $=9000\,J$

$1\,cal=4.5\,J$

$1\,J=\dfrac{1}{4.2\,cal}$

$9000\,J=\dfrac{9000}{4.2}=2142.85\,cal$

$7000\,kilo\,cal$ is required to burn $1\,kg$ mass

To reduce $5\,kg$ mass, energy required $=7000\times 5=35000\,kilo\,val$

Number of trip $=\dfrac{35000\times 1000}{2142.85}=1.7\times 10^{3}$

What is $\Delta E$  for a system that does 5 kcal of work by the surroundings when 3 kcal heat is absorbed by the system.  

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. -2 kcal

  2. +2 kcal

  3. +8kcal

    • 7 kcal
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Correct Option: C

A bullet of mass 10 gm moving with a speed of 20 m/s hits an ice block of mass 990 gm kept on a frictionless floor and gets stuck in it. The amount of ice that melts, if 50% of the lost kinetic energy goes to ice, will be 

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $0.003 g$

  2. $0.30 g$

  3. $0.0003 g$

  4. $3.0 g$

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Correct Option: A

A steel ball of mass $5$ ${ g }$ is thrown downward with velocity $10$ ${ ms } ^ { - 1 }$ from height $19.5$ ${ m }$ . It penetrates sand by $50$ ${ cm }$ . The change in mechanical energy will be ( ${ g } = 10$ ${ ms } ^ { - 2 }$ )

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. $1$ ${J}$

  2. $1.25$ ${J}$

  3. $1.5$ ${J}$

  4. $1.75$ ${J}$

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Correct Option: B
Explanation:

$\begin{array}{l} The\, \, change\, \, in\, \, mechanic\, \, energy\, \, \Delta U=mg\left( { h+x } \right) +\frac { 1 }{ 2 } m{ v^{ 2 } } \ here\, \, m=5g=0.00\, 5kg\cdot h=19.5\, mx=50cm=0.5m,v=10\, m/s \ So,\, \Delta U=0.005\times 10919.5+0.5+\frac { 1 }{ 2 } \times 0.005\times { \left( { 10 } \right) ^{ 2 } }=0.005\times 10\times 20+\frac { 1 }{ 2 } \times 0.005\times 100=1.25J \end{array}$

Hence,
option $(B)$ is correct answer.

A block of ice falls from certain height and completely melts. If only 3/4th of the energy is absorbed by the block the height of fall should be

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. 48.4 m

  2. 84.4m

  3. 88.4m

  4. 44.8m

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Correct Option: D

A block of ice at 0 C whose mass is initially 50.0 kg slides along a horizontal surface starting at a speed of 5.38 m/s and finally coming of ice melted as a result of the friction between the block and the surface will be

physics the essence of change different forms of energy energy conversions energy transformations and energy transfers

  1. 2.16 g

  2. 4.0 g

  3. 1 g

  4. 50 g

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Correct Option: A