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Energy Test - 8

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Energy Test - 8
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  • Question 1
    1 / -0

    A stone is thrown upwards then what will happen?

    Solution

    According to the question the correct option will be ‘C’ because when a stone is thrown upwards, its velocity decreases and height increases.

    K.E. = 12mv2

    P.E. = mgh

    Thus, its kinetic energy decreases and potential energy increases.

  • Question 2
    1 / -0

    Iron glows in red color when it is heated to very high temperature reason behind this reaction is -

    Solution

    Iron glows in red colour when it is heated to very high temperature cause heat energy is being converted into light energy.

  • Question 3
    1 / -0

    Energy transformation takes place in dynamo is a type of-

    Solution

    Dynamo is an electrical generator in which mechanical energy is converted into electrical energy in order to produce direct current.

  • Question 4
    1 / -0

    During photosynthesis, conversion take place by green plants-

    Solution

    According to the question the correct option will be ‘B’ because During photosynthesis, green plants convert light energy into chemical energy stored in the form of food.

  • Question 5
    1 / -0

    A ball falls freely under gravity from rest. label the kind of energy it will possess on reaching the ground.

    Solution

    According to the question the correct option will be ‘B’ because After reaching the ground it will not have any height from the ground hence no potential energy as it is defined as virtue of state of its position where as it has velocity by which it can be said that kinetic energy exists as it is defined by virtue of state of its motion. While falling potential energy keeps on changing in kinetic energy and on reaching the ground all potential energy changes to kinetic energy. Hence there exists only kinetic energy.

  • Question 6
    1 / -0

    Conversion made by a thermocouple -

    Solution

    According to the question the correct option will be ‘D’ because A thermocouple converts heat energy into electrical energy.

  • Question 7
    1 / -0

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

    Solution

    According to the question the correct option will be ‘D’ because when ball is at rest it will have only P.E that is

    P.E= mg h

    M = 2 kg; h = 5 m

    P.E = 2 × 10 × 5 = 100J

    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=100JK.E=100J.

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

  • Question 8
    1 / -0

    In steam engine the conversion process will occur-

    Solution

    According to the question the correct option will be ‘B’ because Heat is used to generate steam which moves the pistons and thereby converting heat energy to mechanical energy.

  • Question 9
    1 / -0

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

    Solution

    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)

  • Question 10
    1 / -0

    chemical energy is converted into heat energy hence the process is called-

    Solution

    According to the question the correct option will be ‘C’ because The chemical present in the candle burns with oxygen to give out heat.

  • Question 11
    1 / -0

    An anti-aircraft shell has been fired which was having kinetic energy x. It explodes in the air. Then the sum of kinetic energies of all the particles will be-

    Solution

    During explosion, the chemical energy gets converted into kinetic energy. So, after explosion sum of kinetic energies of all the particles is greater than the initial kinetic energy.

  • Question 12
    1 / -0

    In case of explosion of a bomb ,does not change-

    Solution

    According to the question the correct option will be ‘B’ because the chemical energy possessed by the bomb after explosion converts into heat energy, sound energy, and light energy i.e. into different forms of energy but remains conserved. Hence, total energy of bomb does not change, but kinetic and mechanical energy changes.

  • Question 13
    1 / -0

    A man of weight 60 kg wants to lose 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 k cal. How many times must he go up and down to reduce his 7 kg weight? (Take g=10ms−2)

    Solution

    According to the question the correct option will be ‘C’ because Energy used to go up = mgh = 60 × 10 × 10 = 6000J

    Energy used to come down 6000J2= 3000J

    Energy used in one round trip = 9000J

    1cal = 4.5J

    1J = 14.2cal

    9000J = 90004.2 = 2142.85cal

    7000kilocal is required to burn 1kg mass

    To reduce 5kg mass, energy required =7000×5=35000 kilo vatt

    Number of trip =35000×10002142.85 = 1.7×103

  • Question 14
    1 / -0

    Which of the following statements is correct?

    Solution

    Answer is A

    Momentum is a vector quantity while K.E is a scalar quantity ,we can change velocity in such a way momentum remains same but K.E changes.

  • Question 15
    1 / -0

    Device that does not convert electrical energy into sound energy is called-

    Solution

    According to the question the correct option will be ‘B’ because a microphone converts sound energy into electrical energy. All other devices mentioned convert electrical energy into sound energy.

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