Final answer:
In a perfectly elastic collision where a particle of mass m makes a head-on collision with a particle of mass 2m initially at rest, the first particle's kinetic energy is completely transferred to the second particle. Hence, the percentage loss of energy of the colliding particle is 100%.
Step-by-step explanation:
The student has asked about the percentage loss of energy of a colliding particle after a head-on elastic collision where a particle of mass m collides with a particle of mass 2m that is initially at rest. In a perfectly elastic collision, the total kinetic energy and momentum are conserved. Given that the mass of the first particle is m and the second particle is 2m, after the collision, the first particle comes to rest and the second particle moves with the velocity the first particle had before the collision.
Since the second particle, having twice the mass of the first, moves off with the original velocity of the first particle, it now has twice the kinetic energy that the first particle had. The first particle's energy has been entirely transferred to the second particle. In other words, the first particle has lost 100% of its kinetic energy to the second particle.
Therefore, the percentage loss of energy of the colliding particle is 100%.