Plastic impact - Conserving momentum

Q.  If a body is subjected to plastic impact, _______
- Published on 21 Sep 15

a. only kinetic energy is conserved
b. only momentum is conserved
c. both a. and b.
d. none of the above

ANSWER: only momentum is conserved


  • Sravanthi   -Posted on 16 Dec 15
    1) Plastic impact:

    - After plastic impact, two objects get joined and move together with common velocity. In these objects, there is no period of restitution due to permanent deformation.

    - During plastic impact, kinetic energy is lost and is not conserved. The coefficient of restitution is zero.

    - Momentum is conserved and the equation is given as

    mAuA + mAuA = v (mA + mB)

    v is the common velocity of objects.

    2) Perfectly elastic impact: When a body undergoes elastic collision, there is no loss of kinetic energy. Kinetic energy and momentum are conserved and the object undergoes complete restoration. Hence, here the coefficient of restitution is one. The objects undergoing perfectly elastic impact separate after facing impact.

    3) Semi-elastic impact: When a body undergoes semi-elastic collision, kinetic energy is not conserved and is less than the kinetic energy before the collision. In this case, the coefficient of restitution lies between 0 and 1 i.e (0 < e < 1)

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