An alert physics student stands beside the tracks as a train rolls slowly past. he notes that the frequency of the train whistle is 496 hz when the train is approaching him and 478 hz when the train is receding from him. using these frequencies, he calculates the speed of the train. what value does he find? (assume the speed of sound in air is 343 m/s.)

Balloon a has charge q, and identical mass balloon b has charge 10q. you hang them from threads near each other. choose all of the statements with which you agree. check all that apply. a. a and b exert the same magnitude forces on each other. b. the force that a exerts on b is 10 times the force that b exerts on a. c. the angle between the thread supporting a and the vertical is < the angle between the thread supporting b and the vertical. d. the force that a exerts on b is 1/10 the force that b exerts on a.