Tag: work, energy and machines

Questions Related to work, energy and machines

The law of conservation of energy implies that the:

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. Total mechanical energy is conserved

  2. Total kinetic energy is conserved

  3. Total potential energy is conserved

  4. Sum of all kinds of energies is conserved

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Correct Option: D
Explanation:

Law of conservation of energy implies that energy can neither be created nor destroyed, but can merely be transfered from one form to other. These forms are varied. Thus, when considering all forms of energy,(including workdone) the total sum never changes.

Energy conservation law says that:

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. Energy can't be destroyed but can be produced.

  2. Neither energy can be produced nor can be destroyed.

  3. Energy can't be produced but can be destroyed.

  4. Energy can be produced and can be destoyed

Show answer
Correct Option: B
Explanation:

In physics, the law of conservation of energy states that the total energy of an isolated system remains constant—it is said to be conserved over time. Energy can neither be created nor destroyed; rather, it transforms from one form to another.

The speed of a car of mass 1000 kg is reduced from 20 m/s to 10 m/s. What is the work done by the brakes of the car?

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. 150 kJ

  2. 120 kJ

  3. 100 kJ

  4. 80 k J

Show answer
Correct Option: A
Explanation:

Work done by the brakes of a car will be the net change in the kinetic energy of car
$W=\dfrac{1}{2}m({v _2}^2-{v _1}^2)$
$W=\dfrac{1}{2}m({10}^2-{20}^2)$
$W=\dfrac{1}{2}m(100-400)$$=$$\frac{1}{2}1000(-300)$
$W=-150000J=-150KJ$
Hence, option A is correct.

When a stone falls freely towards the earth, its total energy ?

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. First decreases and then becomes zero

  2. Remains constant

  3. Increases

  4. Decreases

Show answer
Correct Option: B
Explanation:

Since the ball is in free-fall, the only force acting on it is gravity. Therefore, we can use the principle of conservation of mechanical energy - initially the ball has potential energy and no kinetic energy. As it falls, its total energy (the sum of the KE and the PE) remains constant and equal to its initial PE.
Hence, option B is correct.

In which one of the following is electrical energy is converted to light energy?

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. Radio

  2. Fan

  3. Television

  4. Electric iron

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Correct Option: C
Explanation:

The machine in which electrical energy is converted to light energy is television.

A steam engine converts

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. Chemical energy into heat energy

  2. Heat energy into mechanical energy

  3. Chemical energy into mechanical energy

  4. Mechanical energy into heat energy

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Correct Option: B
Explanation:

A steam engine converts heat energy into mechanical energy.

When an object falls freely towards the earth, then its total energy :

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. Increases

  2. Decreases

  3. Remains constant

  4. Can't say

Show answer
Correct Option: C
Explanation:

Since the ball is in free-fall, the only force acting on it is gravity. Therefore, we can use the principle of conservation of mechanical energy - initially the ball has potential energy and no kinetic energy.
As it falls, its total energy (the sum of the KE and the PE) remains constant and equal to its initial PE.
Hence, option C is correct.

According to law of conservation of energy :

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. Energy can be created but not destroyed and it can be transformed from one form into another

  2. Energy exists in only one form

  3. Energy exists in many forms but it cannot be transformed

  4. Energy can neither be created nor be destroyed but can change into different forms

Show answer
Correct Option: D
Explanation:

The law of conservation of energy states that in a closed system the total amount of energy is conserved and does not change. This means that energy may change from one form to another, but that the total amount of energy in the closed system remains constant. 

So accoding to this statement it is clear that only option D is best possible.

What is law of conservation of energy?

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. Energy can neither be created nor destroyed. It can only be transformed from one to another.

  2. Energy can only be created nor destroyed. It can only be transformed from one to another.

  3. Energy can neither be created but can be destroyed. It can only be transformed from one to another.

  4. None

Show answer
Correct Option: A
Explanation:

Energy can neither be created nor destroyed. It can only be transformed from one to another is the law of conservation of energy. For example , object falling from certain height converts its potential energy to kinetic energy and at all instant total mechanical energy remains constant.

When you push a huge rock with all your might and fail to move it,then:

physics types of energy law of conservation of energy the law of conservation of energy work, energy and machines

  1. transfer of muscular energy to stationary rock does not take place

  2. low transfer of muscular energy to stationary rock take place

  3. high transfer of muscular energy to stationary rock take place

  4. none

Show answer
Correct Option: A
Explanation:

Transfer of muscular energy to stationary rock does not take place as the displacement is zero so the work done by you is zero, avoiding any conversion of energy.