A megnetic dipole with a dipole moment of magnitude `0.020 J/T` is released from rest in a tutiliform magnetic field of magnitude `52 mT`. The rotation of the dipole due to the magnetic force on it is unimpeded. When the dipole rotates through the orientations where its dipole moment is aligned with the magnetic field, its kinetic energy is `0.80 mJ`.
(a) What is the initial angle between the dipole moment and the magnetic field?
(b) What is the angle when the dipole is next (momentarily) at rest?

Explanation

a. From energy conservation
`U_theta=K_theta=U_(0^@)+K_(0^@)`
or `(-Mbcostheta)+0=(-MBcos0^@)+K_(0^@)`
substituting the gien values we can calculate.
b. To other side also it rotates upto the same angle.