Question

Which of the following is not an example of perfectly inelastic collision?
A) A bullet fired into a block, if the bullet gets embedded into the block.
B) Capture of an electron by an atom.
C) A man jumping onto a moving boat.
D) A ball bearing striking another ball bearing.

Answer 1

We need to understand the difference between a perfect elastic collision and a perfect inelastic collision to analyse the given four situations and consider the possibilities of having either a perfectly elastic or inelastic type of collision.

Complete answer:
We can define the two types of collision initially to distinguish between them. Elastic collisions are those collisions in which the kinetic energy of the colliding body is transported to the other body. A perfect elastic collision is the situation in which the complete kinetic energy is transferred without losing any into another form of energy.
An inelastic collision is the phenomenon in which the bodies after collision convert some of the kinetic energy into other forms of energy. In a perfectly elastic collision, the complete kinetic energy is converted to another form of energy.
Now, we can consider each situation with the explanations given above.
A bullet fired into a block loses its complete kinetic energy when it finally stops inside the block. So, it is a perfectly inelastic collision.
A moving electron when captured by an atom loses its kinetic energy completely, so it is also a perfectly inelastic collision.
A man jumping onto a moving boat comes to rest without disturbing the other system, so it is also inelastic.
A ball bearing striking another ball bearing transfers the kinetic energy from one to the other which triggers the latter ball to move. So, the collision is not perfectly inelastic.

The correct answer is option (D).

Note:
We need to understand that the cases of perfect collisions are very hard to be practical, especially the elastic collisions. This is because, the collisions are also dependent on the angles at which they collide to result in perfect and imperfect transfer of energies.