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Science Assertion (A) & Reason (B) MCQ

Work, Power And Energy · Gujarat Board (GSEB) STD 9 (GSEB - English Medium). 5 questions.

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Assertion (A) & Reason (B) MCQ

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5 questions · timed · auto-graded

MCQ 11 Mark
In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
Assertion: Work done by the force of friction is always negative.
Reason: Friction force always acts in opposite direction to that of motion of the body.
  • ✓
    Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
  • B
    The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
  • C
    Assertion is true but the Reason is false.
  • D
    The statement of the Assertion is false but the Reason is true.​​​​​
Answer
Correct option: A.
Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
Yes, the work done by friction is negative because it acts against the force applied. In the same reference frame, kinetic friction is always in the direction opposite the motion, and does negative work.
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MCQ 21 Mark
A statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as Mark the correct choice as: Assertion: Steam engine converts heat energy into kinetic energy.
Reason: Steam engine works on the principle conservation of energy.
  • ✓
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  • B
    If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
  • C
    If Assertion is true, but Reason is false.
  • D
    If Assertion is false, but Reason is true.
Answer
Correct option: A.
If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
steam engine, machine for converting heat energy into mechanical energy using steam as a medium, or working fluid. When water is converted into steam it expands, its volume increasing about 1,600 times. Steam from the other inlet valve then pushes the piston back to its original position, and the cycle starts again.
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MCQ 31 Mark
In the following Questions, the Assertion and Reason have been put forward. Read the statements carefully and choose the correct alternative from the following:
Assertion: Greater the momentum of a body, more is its kinetic energy.
Reason: Kinetic energy is a scalar quantity and momentum is a vector quantity.
  • ✓
    Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
  • B
    The Assertion and the Reason are correct but the Reason is not the correct explanation of the Assertion.
  • C
    Assertion is true but the Reason is false.
  • D
    The statement of the Assertion is false but the Reason is true.​​​​​
Answer
Correct option: A.
Both the Assertion and the Reason are correct and the Reason is the correct explanation of the Assertion.
The momentum of a body is given as the product of its mass and velocity at which it is traveling, whereas the kinetic energy is given as one-half of the product of its mass and the square of the velocity with which it is traveling. Therefore the kinetic energy varies as the square of the momentum.
Kinetic energy is a scalar quantity, it does not have a direction. Unlike velocity, acceleration, force, and momentum, the kinetic energy of an object is completely described by magnitude alone.
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MCQ 41 Mark
A statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as Mark the correct choice as:
Assertion: In a stretched bow, potential energy is stored.
Reason: Mechanical energy of a moving body remains conserved.
  • A
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  • B
    If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
  • ✓
    If Assertion is true, but Reason is false.
  • D
    If Assertion is false, but Reason is true.
Answer
Correct option: C.
If Assertion is true, but Reason is false.
For conservative forces the sum of kinetic and potential energies at any point remains constant throughout the motion.
This is known as law of conservation of mechanical energy. According to this law, Kinetic energy + Potential energy = constant or,
$\triangle\text{K}+\triangle\text{U}=0$ or
$\triangle\text{K}=-\triangle\text{U}$
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MCQ 51 Mark
A statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as Mark the correct choice as: Assertion: Work done by a body is zero only when, displacement produced by the force is zero.
Reason: Work done by a force is negative when, displacement occurs in the direction of applied force.
  • A
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  • B
    If both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
  • C
    If Assertion is true, but Reason is false.
  • ✓
    If Assertion and Reason both are false.
Answer
Correct option: D.
If Assertion and Reason both are false.
Work can be either positive or negative: if the force has a component in the same direction as the displacement of the object, the force is doing positive work. If the force has a component in the direction opposite to the displacement, the force does negative work.
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