15. A drum corps can be heard practicing at a distance of 1.6 km (about 1 mile) from the field, What is the time delay between the drumstick hitting the drum and the sound heard by an
individual 1.6 km away? (Assume the speed of sound in air to be 340 m/s.)

Ametal ring 4.20 cm in diameter is placed between the north and south poles of large magnets with the plane of its area perpendicular to the magnetic field. these magnets produce an initial uniform field of 1.12 t between them but are gradually pulled apart, causing this field to remain uniform but decrease steadily at 0.240 t/s . (a) what is the magnitude of the electric field induced in the ring? (b) in which direction (clockwise or counterclockwise) does the current flow as viewed by someone on the south pole of the magnet?