Two very small spherical metal objects, each with 1 coulomb of charge, are brought together in a vacuum so that the separation distance between their centers is 1 mm. what is the force of repulsion between the two object? (coulomb's constant is k=9.0 × 109 n. m2/c2.)

Air is to be preheated by hot exhaust gases in a cross-flow heat exchanger before it enters the furnace. air enters the heat exchanger at 95 kpa and 20°c at a rate of 0.6 m^3/s. the combustion gases (cp = 1.10 kj/kg°c) enter at 160°c at a rate of 0.95 kg/s and leave at 95°c. determine the rate of heat transfer to the air and its outlet temperature.