一條物理熱學問題和一條物理力學問題

1. The temperature of the room air rises because there is energy input into the room from the electrical power. Thus, just by comparing energy content of the room before and after the supply of electrical power, the energy content of the room has increased. Assume no energy lost from the room, this increase of energy is transformed to heat which causes a rise in temperature of the room air.
As a result of the temperature rise, the pressure of air will increase according to the Pressure Law (a special form of the ideal gas law).
2. Without involving in detailed calculation, electric force is generally stronger than gravitational force. Since the electric force is acting upward, when the ball goes up along a vertical circle, its electrical potential energy (PE) decreases.
Thus, when the ball moves up, it loses electrical potnetial energy but gain in gravitational potential energy. Since the loss of electrical PE is greater than the gain in gravitational PE, there is a net decrease of PE, its kinetic energy and hence velocity will increase. Therefore, the velocity of the ball at the highest point (which has the minimum net PE) is smaller than that at the lowest point (which has the maximum net PE).
At the highest point, the strong electric force is pointing upward, there must be a (downward) tension in the string in order to counterbalance the upward electric force, as the downward gravitational force is weak as compared with the electric force. The string tension will not be zero.