Acar approaches a train-crossing bell at speed v. the bell has a perceived frequency f1. after the car passes the bell, the driver hears a frequency f2. the two frequencies are in the ratio of 7: 6 (or 6: 7, depending on how you order them).
(a) which frequency will be higher, f1 or f2?
(b) if the speed of sound is 340 m/s, what is the car speed v?

With i really need the correct answer!

Which changes of state do the labels represent? a: b: c:

Electric field of the earth. the earth has a net electric charge that causes a field at points near its surface equal to 150 n> c and directed in toward the center of the earth. (a) what magnitude and sign of charge would a 60-kg human have to acquire to overcome his or her weight by the force exerted by the earth’s electric field? (b) what would be the force of repulsion between two people each with the charge calculated in part (a) and separated by a distance of 100 m? is use of the earth’s electric field a feasible means of flight? why or why not?