A short bar magnet of magnetic moment ${\text{0.8\hspace{0.33em}JT}}^{\text{-1}}$ is placed in a uniform magnetic field of $\text{0.32\hspace{0.33em}T}$ . The magnet is in stable equilibrium when the potential energy is:

Here magnetic moment  ${\text{M=0.8\hspace{0.33em}JT}}^{-1}$
Magnetic field  $\text{B=0.32\hspace{0.33em}T}$
When a bar magnet is placed in a uniform magnetic field; its potential energy

 $\mathrm{U}=-\overrightarrow{\mathrm{M}}. \overrightarrow{\mathrm{B}}$
 $\text{⇒U=-MBcos}\mathrm{\theta }$
For stable equilibrium  $\mathrm{\theta }=0$
$\text{⇒U=-MB}$ 
$\text{⇒U=-0.8}\times \text{0.32}$ 
$\text{⇒U=-0.256\hspace{0.33em}J}$ .