Tag: energy transformations and energy transfers

Questions Related to energy transformations and energy transfers

A metal ball of mass $2kg$ is allowed to fall freely from rest from a height of $5m$ above the ground (Take $g=10ms^{-2}$). After the ball hits the ground and comes to rest, mechanical energy is converted to:

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

  1. heat energy

  2. sound energy

  3. electrical energy

  4. Both A & B

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Correct Option: D
Explanation:

When ball is at rest it will have only P.E that is
$P.E = mgh$


$m = 2\  kg; h = 5\  m$

$P.E = 2\times 10\times 5 = 100 J$

This is the total energy as K.E is zero when ball is at maximum height that is when it is at 5m. Hence when ball reaches the ground P.E becomes zero  because height is zero. At this point total energy is equal to K.E that is $K.E = 100 J$.

This $100\  J$ will convert to heat and sound energy as the ball comes to rest.

State whether the given statement is True or False :

A freely falling object eventually stops on reaching the ground. A part of the kinetic energy on reaching the ground changes into heat energy.

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

  1. True

  2. False

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Correct Option: A
Explanation:

The kinetic energy on reaching the ground changes into heat energy, sound energy, etc. and therefore gets dissipated to the ground and air.

Iron glows in red colour when it is heated to very high temperature because:

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

  1. Heat we supply consumes red colour at high temperature

  2. Mechanical energy is being converted into heat energy

  3. Light energy is being converted into heat energy

  4. Heat energy is being converted into light energy

Show answer
Correct Option: D
Explanation:

Iron glows in red colour when it is heated to very high temperature because heat being a form of energy can be transformed into other forms of energy.

A moving coin hits another coin and sets it into motion.In this case energy from the moving coin is ---- to the other coin:

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

  1. Flown

  2. Taken

  3. Not transferred

  4. Transferred

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Correct Option: D
Explanation:

The moving coin has kinetic energy initially, after hitting the other coin it transfers its kinetic energy to the other coin and sets it in motion.(In reality some part of energy is also lost as heat energy)

When a stone is thrown upwards:

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

  1. Kinetic energy increases and Potential energy decreases

  2. both Kinetic energy and Potential energy increase

  3. Kinetic energy decreases and Potential energy increases

  4. both remain constant

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Correct Option: C
Explanation:

When a stone is thrown upwards, its velocity decreases and height increases. 

$K.E. = \dfrac{1}{2}{ mv }^{ 2 }$
$P.E. = mgh$
Thus, its kinetic energy decreases and potential energy increases.

In which of the following, chemical energy is converted into heat energy?

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

  1. Heater

  2. Refrigerator

  3. Candle

  4. Motor

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Correct Option: C
Explanation:

The chemical present in the candle burns with oxygen to give out heat.

Which of the following statement is NOT true?

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

  1. State of rest of a body is same as the state of zero speed

  2. Human body converts chemical energy into muscular energy

  3. Water in river flows down due to its kinetic energy

  4. Liquids exert pressure on the walls of the container

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Correct Option: C
Explanation:

Option C is not correct because river flows down due to its gravitational potential energy.

In steam engine:

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

  1. Mechanical energy is converted to heat energy

  2. Heat energy is converted to mechanical energy

  3. Heat energy is converted to electrical energy

  4. Heat energy is converted to chemical energy

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Correct Option: B
Explanation:

Heat is used to generate steam which moves the pistons and thereby converting heat energy to mechanical energy.

A tube light converts electrical energy into :

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

  1. Chemical energy

  2. Magnetic energy

  3. Light energy

  4. Mechanical energy-

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Correct Option: C
Explanation:

A tube light converts $Electrical  \ energy$ to $Light  \ Energy$.

The device / machine which converts chemical energy into electrical energy is

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

  1. Electric bulb

  2. Electric motor

  3. Battery

  4. Solar cell

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Correct Option: C
Explanation:

Option A: Electrical bulb converts electrical energy into heat.

Option B: electrical motor converts electrical energy in mechanical energy.
Option C : battery converts chemical emergy into electrical energy.
Option D: solar cell converts light (using photons) into electrical energy.
So best possible answer is option C.