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Work, Energy and Power Test - 20

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Work, Energy and Power Test - 20
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  • Question 1
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion : A work done by friction is always negative.

    Reason : If frictional force acts on a body its K.E. may decrease.

    Solution

    When frictional force is opposite to velocity, kinetic energy will decrease.

  • Question 2
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion : A force applied on the body always does work on the body.

    Reason : If a force applied on a body displaces the body along the direction of force work done will be maximum.

    Solution

    If force is acting on a body work done can be zero. When an object is at rest and no external force except gravity is acting on it in this case the work that would be zero as the force acting on it is perpendicular.

  • Question 3
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion : The work done in moving a body over a closed loop is zero for every force in nature.

    Reason : Work done depends on nature of force.

    Solution

    In close loop, s = 0, and so W = Fs = 0.

  • Question 4
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion : The change in kinetic energy of a particle is equal to the work done on it by the net force.

    Reason : Change in kinetic energy of particle is equal to work done only in case of a system of one particle.

    Solution

    Change in kinetic energy = work done by net force. This relationship is valid for particle as well as system of particles.

  • Question 5
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion: Kinetic energy of a body is quadrupled, when its velocity is doubled.

    Reason : Kinetic energy is proportional to square of velocity. If velocity is doubled the K.E. will be quadrupled

    Solution

    When velocity is doubled

    K=1/2(mv2) becomes K’ = 1/2(m(2v)2) = 4[1/2(mv2)]

    So KE becomes four times

  • Question 6
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion: If the velocity of a body is tripled, then K.E. becomes 9 times.

    Reason : Kinetic energy , K.E.=mv2/2

    Solution

  • Question 7
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion: Kinetic energy of a system can be increased or decreased without applying any external force on the system.

    Reason: This is because K.E. =mV2/2, so it independent of any external forces.

    Solution

    K.E. can be increased or decreased without applying any external force, as internal forces can do work e.g., explosion of a bomb.

  • Question 8
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion : The rate of change of total momentum of a many particle system is proportional to the sum of the internal forces of the system.

    Reason : Internal forces can change the kinetic energy but not the momentum of the system.

    Solution

    Rate of change of momentum is proportional to external forces acting on the system. The total momentum of whole system remain constant when no external force is acted upon it. Internal forces can change the kinetic energy of the system.

  • Question 9
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion : A man rowing a boat upstream is at rest with respect to the bank. He is doing no external work.

    Reason : Work done by constant force, W = F s cosθ.

    Solution

    In this case, s = 0, and so W = 0.

  • Question 10
    1 / -0

    Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.

    Assertion : A spring has potential energy, both when it is compressed or stretched.

    Reason : In compressing or stretching, work is done on the spring against the restoring force.

    Solution

    Work done on the spring is stored in the spring in the form of potential energy as restoring force is always opposite to applied force.

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