A hot air balloon and its basket together weigh 300 N and it contains hot air weighing 17000 N. If the lift capacity of the balloon is 5000 N, What is the weight of the cold air displaced by the balloon and its basket?

Students in an introductory physics lab are performing an experiment with a parallel-plate capacitor made of two circular aluminum plates, each 11 cm in diameter, separated by 1.0 cm. how much charge can be added to each of the plates before a spark jumps between the two plates? for such flat electrodes, assume that value of 3×106n/c of the field causes a spark.