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Show that internal forces can change the...

Show that internal forces can change the kinetic energy but not linear momentum .

Text Solution

Verified by Experts

`vecF_("ext") = M veca_(CM) implies vecF_("ext") = (M d vecv_(CM))/(dt)`
`vecF_("ext") = (d)/(dt) (M vecv_(CM))`

Only external forces can change the momentum of a system . Internal forces can gives rise to kinetic energy . A compressed spring attached to two blocks , converts its potential energy into kinetic energy . This K.E. is due to internal forces .
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Internal force can change

Choose the correct statement regarding a system of particles. Internal forces can change the kinetic energy of the system without changing system's momentum O Impulse can be defined as a very large force that acts for a very short time and causes finite change in momentum. Internal forces can change the potential energy of the system without changing system's momentum Internal forces can change the mechanical energy of the system without changing system's momentum.

Knowledge Check

  • A : Internal forces can change the kinetic energy but not the momentum of the system. R : The net internal force on a system is always zero.

    A
    If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
    B
    If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
    C
    If Assertion is true statement but Reason is false, then mark (3).
    D
    If both Assertion and Reason are falsė statements, then mark (4).

  • Consider the following statements I. The rate of change of the total linear momentum of a system consisting of many particles is proportional to the vector sum of all the internal forces due to inter-particle interaction. The internal forces can change the kinetic energy of the system of particles are not the linear momentum of the system. Choose the correct option.

    A
    Only I
    B
    Only II
    C
    I and II
    D
    None of these

  • Assertion: Internal forces cannot change linear momentum. Reason: Internal forces can change the kinetic energy of a system.

    A
    (a) If both Assertion and Reason are true and the Reason is correct explanation of the Assertion.
    B
    (b) If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
    C
    (c) If Assertion is true, but the Reason is false.
    D
    (d) If Assertion is false but the Reason is true.

    • Similar Questions

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    CRTM Kinetic Energy and Angular Momentum

    Point out the correct alternative : (a) When a conservative force does positive work on a body , the potential energy of the body increases // decreases // remains unaltered. (b) Work done by a body against friction always result in a loss of its kinetic // potential energy. (c) The rate of change of total momentum of a many particle system is proportional to the external force // sum of the internal forces of the system. (d) In an inelastic collision of two bodies, the quantities which do not change after the collision are the total kinetic energy // total linear momentum // total energy of the system ot two bodies.

    Underline the correct alterntaive: a) when a conservative force does positivie work on a body, the potential energy of the body increase/decreases/remains unaltered. work done by a body against friction always results in a loss of its kinetic /potential energy. c) The rate of change of total momentum of a many-particle system is proportional to the external force/ sum of the internal forces on the system. d) In an inelastic collision of two bodies, the quantities which do not change after the collision are the total kinetic energy/total linear momentum/total enregy of the system of two bodies.

    Assertion : Internal forces acting on the system cannot change linear momentum of the system . Reason : Internal forces can change kinetic energy of the system.

    Statement-1 : Internal forces can change total linear momentum of system. Statement-2 : Due to work of internal forces kinectic energy of system may change.

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