Aconducting bar slides without friction on two parallel horizontal rails that are 50 cm apart and connected by a wire at one end. the resistance of the bar and the rails is constant and equal to 0.10 ω. a uniform magnetic field is perpendicular to the plane of the rails. a 0.080-n force parallel to the rails is required to keep the bar moving at a constant speed of 0.50 m/s. what is the magnitude of the magnetic field?

Atrain is traveling at 30.0 m/s relative to the ground in still air. the frequency of the note emitted by the train whistle is 262 hz. the speed of sound in air should be taken as 344 m/s. what frequency (f approach) is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and approaching it? what frequency (f recede) is heard by a passenger on a train moving at a speed of 18.0 m/s relative to the ground in a direction opposite to the first train and receding from it?