\(\mathrm{W}_{\text {ext }} =\Delta \mathrm{U}+\Delta \mathrm{KE} \quad(\mathrm{P} . \mathrm{E} .=-\overrightarrow{\mathrm{M}} \cdot \overrightarrow{\mathrm{B}})\)
\(=-\overrightarrow{\mathrm{M}} \cdot \overrightarrow{\mathrm{B}}_{\mathrm{f}}+\overrightarrow{\mathrm{M}} \cdot \overrightarrow{\mathrm{B}}_{\mathrm{i}}+0\)
\(=-\mathrm{MB} \cos 90+\mathrm{MB} \cos 0\)
\(=\mathrm{MB}\)
\(=\mathrm{NIAB}\)
\(=200 \times 100 \times 10^{-6} \times \frac{5}{2} \times 10^{-4} \times 1=5 \mu\)