A 30 gram ball rolls along a flat surface at a constant speed in the same direction over 4 meters in 20 seconds. Which is the speed of the ball? (speed = distance = time)
A. 0.2 meters per second
OB. 0.5 meters per second
c. 20 meters per second
D. 80 meters per second

Please answer this FAST!

Electromagnetic induction. a coil of wire contains n turns and has an electrical resistance r. the radius of each turn is a. initially, inside the coil there exists a uniform magnetic field of magnitude b0 parallel to the axis of the coil. the magnetic field is then reduced slowly. the current induced in the coil is i. how long does it take for the magnitude of the uniform field to drop to zero?