physics mc (heat)

1. (1) is wrong because internal energy comprises kinetic energy and potential energy of molecules making up the substance. The potential energy depends on intermolecular force between molecules and which, in turn, depends on the molecular structure of and arrangment within the substance.

The gold piece and fire (which refers to the gas substance in burning) are of different materials and their molecules posses different potential energy at the same temperature. Therefore, the inertnal energy of them are not the same.

(2) is right. At thermal equilibrium, both substances are maintained at the same temperature. If not, heat will flow from the one at higher temperature to the one at lower temperature until the temperatures of them are equal.

(3) is right. When the gold piece expands, separation between molecules increases. Since the larger the molecular separation, the higher the potential energy. As a result, the potential energy of molecules also increase.
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2. Potential energy lost by the falling copper ball = mgd
where g is the acceleration due to gravity

Heat gained by the ball on impact with the ground = m.c.t
where c is the specific heat capacity of copper

Since there is no heat lost to the surroundings, all the released potential energy is absorbed by the ball, thus
m.g.d = m.c.t
i.e. c = gd/t

1.(1) internal energy= potential energy+ kinetic energy
Gold & the flame will have the same temperature eventually: same K.E.
But theyhave different P.E.

(2)The transfer of heat stops when they reach the same temperature=>same temperature

(3) Heatind=> distance between particles increases => P.E. increases

~(2) & (3) => D
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2. E=mgh=mct
gh=ct
c=gh/t

~D

2008-10-19 21:32:26 補充：
1. (1) 佢地different P.E. 係因為唔同material