Why is there no change in the temperature when the process of melting takes place?
a) because the supplied heat is used to overcome the force of attraction between the molecules.
b) because the supplied heat is used to increase the movement between the molecules.
c) because the supplied heat is used to increase the kinetic energy of the molecules.
d) because the supplied heat is used to overcome the force of repulsion between the molecules.
e) because the supplied heat is used to decrease the kinetic energy of the molecules.

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Hot air balloons float in the air because of the difference in density between cold and hot air. in this problem, you will estimate the minimum temperature the gas inside the balloon needs to be, for it to take off. to do this, use the following variables and make these assumptions: the combined weight of the pilot basket together with that of the balloon fabric and other equipment is w. the volume of the hot air inside the balloon when it is inflated is v. the absolute temperature of the hot air at the bottom of the balloon is th (where th> tc). the absolute temperature of the cold air outside the balloon is tc and its density is ďc. the balloon is open at the bottom, so that the pressure inside and outside the balloon is the same. as always, treat air as an ideal gas. use g for the magnitude of the acceleration due to gravity.

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