In being served, a tennis ball is accelerated from rest to a speed of 42.1 m/s. The average power generated during the serve is 2920 W. Assuming that the acceleration of the ball is constant during the serve, find the force acting on the ball.

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?