Why can ultrasound not be heard by humans?

What are similarities and differences of reflection, refraction, diffraction and absorption?

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?

While the change in blank will remain the same during a collision, the force needed to bring an object to a stop can be blank if the time if collision is blank