# Elastic impact - Coefficient of restitution

Q.  What is the coefficient of restitution (e) for elastic impact?
- Published on 18 Sep 15

a. e = 0
b. e = 1
c. e < 0
d. e > 1

#### Discussion

• Sravanthi   -Posted on 16 Dec 15
- The range for coefficient of restitution lies is between 0 ≤ e ≤ .

Coefficient of restitution is defined as the ratio of impulse during restoration period to impulse during deformation period

- The coefficient of restitution depends upon the type of impact. Different types of impacts are as follows:

1) 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.

2) 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)

3) Plastic impact: When a body undergoes plastic impact, it does not restore to its original position but momentum is conserved. Due to impact, the body or object has major loss of kinetic energy. In this case, coefficient of restitution is zero. The objects after plastic impact move with common velocity.

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