P. 3955. There are two samples of gas in a thermally insulated cylinder. One of them is Argon at a temperature of 300 K, and the other is Nitrogen at a temperature of 400 K. There is a thermally insulated wall between them. The two gases have the same pressure and the same volume. Then the wall between the gases is taken away, and the two gases mix.
a) Does the energy of the system change?
b) What will be the common temperature?
c) How does the pressure change?
d) Does the entropy of the system change?
P. 3960. A vertical cylinder of radius R is fixed on a horizontal, ideally smooth tabletop. There is a string attached to the bottom of the cylinder, while to the other end of the string a small disc, whose mass is m, is fixed. The small disc is given a velocity v0 which is perpendicular to the tightened string. The disc slides on the tabletop while the string is wound round the cylinder. a) What is the velocity of the small disc when it hits the wall of the cylinder? (Give both the direction and the magnitude.) b) What is the tension at this moment? (Data: R=1 m, l0=2 m, r=2 cm, m=5 g.)