# Entropy change in an inelastic collision.

1. Sep 29, 2009

### bbhill

1. A 3 kg mass hits a stationary mass of 9 kg and sticks. What is the change in entropy?

So, I figure that I will need to $$\Delta$$S = $$\Delta$$Q$$/$$T.

However, I don't know the heat or the temperature of this reaction, so this couldn't possibly be the way to evaluate.

So, I think I could use S = k ln (number of microstates) and find the difference between the initial and final values of S. However, how would I calculate the number of microstates for this system?

2. Sep 29, 2009

### kuruman

Inelastic collisions do not conserve kinetic energy. Here, the kinetic energy after the collision is less than before. However, total energy is always conserved. So, to what kind of energy is the lost kinetic energy transformed?