When a bar magnet of dipole moment m is placed in a uniform magnetic field B

The total force on the dipole would be zero. 

torque is given by 

$\mathrm{T}=\overrightarrow{\mathrm{m}}\times \overrightarrow{\mathrm{B}}=\mathrm{MB}\mathrm{sin\theta }$

Potential Energy is given by 

$U=-\overrightarrow{M}.\overrightarrow{B}=MB\cos \theta$