A boy whirls a ball on a string in a horizontal circle of radius 0.6 m. If the ball is traveling at 9 m/s, what is the centripetal acceleration? a)135 m/s2
b)62.5 m/s2
c)72 m/s2
d)90 m/s2
e)24 m/s2

The magnetic field inside a superconducting solenoid is 4.50 t. the solenoid has an inner diameter of 6.20 cm and a length of 26.0 cm. determine (a) the magnetic energy density in the field and (b) the energy stored in the magnetic field within the solenoid.