In a brake test, the DC motor took 20 A from a 200 V supply mains. The brake pulley of radius 10 cm had an effective load of 20 kg and the speed was 10 rps. The value of BHP (in metric) is _________.

Correct option is C

$$\text{Given that} \\I = 20\,A, \quad V = 200\,V, \quad r = 10\,cm = 0.1\,m, \quad m = 20\,kg, \quad n = 10\,r.p.s \\[6pt]\text{Torque} = \text{Force} \times \text{Effective radius} \\[6pt]T = 20 \times 9.81 \times 0.1 \quad (\because F = m \cdot g) \\[4pt]T = 19.62\,N\!-\!m \\[8pt]\therefore P = T \times \omega \\[6pt]P = T \times 2\pi n \\[6pt]P = 19.62 \times 2 \times \pi \times 10 \\[6pt]P = 392.4\pi \,\text{watt} \\[6pt]P = \dfrac{392.4\pi}{735.5} \,\text{H.P.} \\[6pt]P = 0.5\pi$$​​