# Thermochemistry

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Suppose a 0.17-kg billiard ball is rolling down a pool table with an initial speed of 4.5 m/s. As it travels, it loses some of its energy as heat. The ball slows down to 3.5 m/s and then collides straight-on with a second billiard ball of equal mass. The first billiard ball completely stops and the second one rolls away with a velocity of 3.5 m/s. Assume the first billiard ball is the system.

Calculate w for the process.

Calculate q for the process.

Calculate delta E for the process.

• Thermochemistry - ,

What is w? How can only one ball be "the system" ?

The collision is elastic since the balls have equal mass and exchange velocities. The only time kinetic energy is lost is when the originally moving ball slows down. The lost energy as the ball slows from 4.5 to 3.5 m/s is converted to heat.

• Thermochemistry - ,

w is work

• Thermochemistry - ,

The work is done against friction while the ball slows down. Consider it equal to the loss of kinetic energy

• Thermochemistry - ,

Transfer of energy from one ball to another during collision is an interesting process. It is done by transferring stress waves, but there must be some motion of the balls during contact to allow work to be done on the other ball.