5. Alcohol, because the linear expansion coefficient is highest.
6. L = 1000 (1 + 1,1 * 10-5 x 40) = 1000,44 m, so it has expanded
0,44 m or 44 cm.
7. If they didn't use expansion joints, there could be potential distortion or breaks.
8. The flame is to heat the helium gas. This way the gas expands and the balloon goes up in the air.