The air also contained a small amount of argon. As the temperature of the air decreased from 20 °C to -190 °C the argon changed
from a gas to a liquid to a solid.
Explain the changes in the arrangement and movement of the particles of the argon
as the temperature of the air decreased.
[6 marks]

The man of mass m1 and the woman of mass m2 are standing on opposite ends of the platform of mass m0 which moves with negligible friction and is initially at rest with s = 0. the man and woman begin to approach each other. derive an expression for the displacement s of the platform when the two meet in terms of the displacement x1 of the man relative to the platform.