9th Class Science Work and energy Question Bank

done Work and Energy Total Questions - 20

• question_answer1)
  A boy of mass 50 kg runs up a flight of 120 stairs, each measuring a height of 25 cm, in one minute and 40 seconds. If \[g\text{ }=\text{ }10\text{ }m\text{ }{{s}^{-2}}\], the power of the boy is
  A)
  150 W              done clear
  B)
  750 W  done clear
  C)
         500 W  done clear
  D)
         250 W done clear
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• question_answer2)
                          Water falls from a height of 60 m at the rate of 15 kg/s to operate a turbine. The losses due to frictional forces are 10% of energy. How much power is generated by the turbine? \[(g=10\text{ }m/{{s}^{2}})\]
  A)
  12.3 kW           done clear
  B)
         7.0 kW done clear
  C)
         8.1 kW done clear
  D)
         10.2 kW                       done clear
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• question_answer3)
  A body of mass 2 kg is thrown up vertically with a kinetic energy of 490 J. If the acceleration due to gravity is \[9.8\text{ }m\text{ }{{s}^{-2}}\], the height at which the kinetic energy of the body becomes half of the original value is
  A)
  50 m    done clear
  B)
         25 m    done clear
  C)
         12.5 m done clear
  D)
         10 m. done clear
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• question_answer4)
  Read the given statements and select the correct option.

  Statement 1: If a light body and a heavy body possess the same momentum, the lighter body will possess more kinetic energy.

  Statement 2: The kinetic energy of a body varies as the square of its velocity.

  A)
  Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1. done clear
  B)
  Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1. done clear
  C)
  Statement 1 is true but statement 2 is false. done clear
  D)
  Both statements 1 and 2 are false. done clear
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• question_answer5)
  Coolie A takes 1 min to raise a box of mass m through a height of 2.0 m. Another coolie 6 takes 30 s for the same job. Which one has greater power?
  A)
  Coolie A done clear
  B)
  Coolie B done clear
  C)
  Both have the same power done clear
  D)
  Cannot say done clear
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• question_answer6)
  Read the given statements and select the correct option.

  Statement 1: A man carrying a bucket of water and walking on a rough level road with a uniform velocity does no work while carrying the bucket.

  Statement 2 : The work done on a body by a force (F) in giving it a displacement (S) is defined as \[W=\overline{F}\cdot \overline{S}=FS\,\,\,\cos \theta \], where \[\theta \] is the angle between vectors \[\overline{F}\] and\[\overline{S}\].

  A)
  Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1. done clear
  B)
  Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1. done clear
  C)
  Statement 1 is true but statement 2 is false. done clear
  D)
  Both statements 1 and 2 are false. done clear
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• question_answer7)
  Match the columns and select the correct option from the codes given below.

  Column I	Column II
  (a) Work done by all the forces	(i) Change in potential energy
  (b) Work done by conservative forces	(ii) Change in kinetic energy
  (c) Work done by external forces	(iii) change in mechanical energy
  (d) Work done in uniform velocity	(iv) Zero

   
  A)
  (a) - (ii), (b) - (i), (c) - (iii), (d) - (iv) done clear
  B)
  (a) - (i), (b) - (iii), (c) - (iv), (d) - (ii) done clear
  C)
  (a) - (iii), (b) - (iv), (c) - (ii), (d) - (i) done clear
  D)
  (a) - (iv), (b) - (ii), (c) - (i), (d) - (iii) done clear
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• question_answer8)
  Four forces of equal magnitude are acting on an object as shown in figure. Which of the following forces does the least work?
  A)
  P                                  done clear
  B)
  Q                     done clear
  C)
  R                      done clear
  D)
         S                      done clear
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• question_answer9)
  A truck and a car having equal kinetic energies are stopped by applying equal retarding force. If \[{{S}_{1}}\] and \[{{S}_{2}}\] are the distances covered by truck and car respectively, before stopping, then
  A)
  \[{{S}_{1}}={{S}_{2}}\]                done clear
  B)
  \[{{S}_{1}}>{{S}_{2}}\] done clear
  C)
  \[{{S}_{1}}<{{S}_{2}}\]    done clear
  D)
         Cannot say done clear
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• question_answer10)
  A particle of mass \[{{M}_{1}}\] is moving with a velocity \[{{v}_{1}}\], and another particle of mass\[{{M}_{2}}\], is moving with a velocity \[{{v}_{2}}\]. Both of them have the same momentum but their different kinetic energies are \[{{E}_{1}}\] and \[{{E}_{2}}\] respectively. If mass \[{{M}_{1}}\] is greater than mass \[{{M}_{2}}\] then
  A)
  \[{{E}_{1}}\] is greater than \[{{E}_{2}}\] done clear
  B)
  \[{{E}_{1}}\] is less than \[{{E}_{2}}\] done clear
  C)
  \[{{E}_{1}}\] is equal to \[{{E}_{2}}\] done clear
  D)
  Ratio of \[{{E}_{1}}\] and \[{{E}_{2}}\] is equal to ratio of \[{{M}_{1}}\]and \[{{M}_{2}}\] done clear
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• question_answer11)
  A graph of the total energy of a freely falling body from a height is
  A)
       done clear
  B)
  done clear
  C)
           done clear
  D)
           done clear
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• question_answer12)
  Read the given statements and select the correct option.

  Statement 1: If a rocket explodes in mid air, its kinetic energy increases.

  Statement 2: Chemical energy of the fuel provides additional kinetic energy to the fragments.

  A)
  Both statements 1 and 2 are true and statement 2 is the correct explanation of statement 1. done clear
  B)
  Both statements 1 and 2 are true but statement 2 is not the correct explanation of statement 1. done clear
  C)
  Statement 1 is true but statement 2 is false.     done clear
  D)
  Both statements 1 and 2 are false.       done clear
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• question_answer13)
  Consider the following statements and select the correct option which identifies true (T) and false (F).

  (i)  When a body thrown up, its kinetic energy gradually changes into potential energy.

  (ii) When a body falls from a certain height, its potential energy remains the same.

  (iii) If two unequal masses have the same momentum, then the heavier body possesses lesser kinetic energy.

   
  A)

  (i)	(ii)	(iii)
  T	F	T

    done clear
  B)

  (i)	(ii)	(iii)
  F	T	F

    done clear
  C)

  (i)	(ii)	(iii)
  T	T	F

    done clear
  D)

  (i)	(ii)	(iii)
  F	F	T

    done clear
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• question_answer14)
  Potential energy of an object at a height h is\[{{E}_{p}}=mgh\]. This equation is true only if

  (i) The acceleration due to gravity is constant.

  (ii) The potential energy is path dependent.

   
  A)
  Only (i) is true. done clear
  B)
  Only (ii) is true. done clear
  C)
  Both (i) and (ii) are false done clear
  D)
  Both (i) and (ii) are true. done clear
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• question_answer15)
  A skier of mass 50 kg stands at point P at the top of the ski jump and moves from P to Q and takes off his jump at Q as shown in figure. If 50% of the change in the gravitational potential energy of the skier between points P and Q becomes the kinetic energy at Q then the speed at which the skier arrives at Q is
  A)
  \[10\text{ m }{{\text{s}}^{-1}}\]                 done clear
  B)
  \[20\text{ m }{{\text{s}}^{-1}}\]     done clear
  C)
         \[30\text{ m }{{\text{s}}^{-1}}\]     done clear
  D)
         \[40\text{ m }{{\text{s}}^{-1}}\] done clear
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• question_answer16)
  A mass of M kg is suspended by a weightless string. The horizontal force that is required to displace it until the string making an angle of \[45{}^\circ \] with the initial vertical direction is
  A)
  \[Mg(\sqrt{2}-1)\]                    done clear
  B)
  \[Mg(\sqrt{2}+1)\]      done clear
  C)
  \[Mg\sqrt{2}\]  done clear
  D)
         \[\frac{Mg}{\sqrt{2}}\] done clear
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• question_answer17)
  A body moves under a variable force. For the body a plot of velocity versus time is shown in figure. The correct statement is
  A)
  In moving from C to D, work done by the force on the body is positive done clear
  B)
  In moving from 6 to C, work done by the force on the body is positive done clear
  C)
  In moving from A to B, the body does work on the system done clear
  D)
  In moving from O to A, work done by the body and is negative. done clear
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• question_answer18)
  Two inclined frictionless tracks, one gradual and the other steep meet at point A from where two stones (I and II) are allowed to slide down from rest, one on each track as shown in figure. Which of the following statements is correct?
  A)
  Both the stones reach the bottom at the same time but not with the same speed. done clear
  B)
  Both the stones reach the bottom with the same speed and stone I reaches the bottom earlier than stone II. done clear
  C)
  Both the stones reach the bottom with the same speed and stone II reaches the bottom earlier than stone I. done clear
  D)
  Both the stones reach the bottom at different times and with different speeds. done clear
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• question_answer19)

  The diagram shows a cyclist moving down a small hill at P before travelling on a flat road at Q. The total mass of the cyclist and his bicycle is 60 kg and the speed of the cyclist at P is\[10\text{ m}{{\text{s}}^{-1}}\].

  Which of the following is incorrect?

   
  A)
  The kinetic energy at P is 3000 J. done clear
  B)
  The loss of gravitational energy between P and Q is 1800 J. done clear
  C)
  Total energy is 4800 J. done clear
  D)
  The cyclist does not require a greater power when he travels at a higher constant speed. done clear
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• question_answer20)
  The diagram shows an object released from point X and travelling on a frictionless track. If a heavier object is taken in consideration then

  (i) It will move with a greater speed at Y.

  (ii) The speed of the object at M is\[10\text{ m}{{\text{s}}^{-1}}\].

   
  A)
  Only (i) is true. done clear
  B)
  Only (ii) is true. done clear
  C)
  Both (i) and (ii) are true. done clear
  D)
  Neither (i) nor (ii) is true. done clear
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