A train 100 m long crosses a pole in 5 seconds. Its speed in km/h is
A. 72 km/h
B. 36 km/h
C. 20 km/h
D. 50 km/h
Answer: Option A
Solution (By JKSSB Mock Tests)
Speed = distance/time = 100 m / 5 s = 20 m/s. Convert to km/h: multiply by 18/5 => 20 × 18/5 = 72 km/h. Pole is a point, so train's own length is the distance crossed. Speed in km/h = m/s × (18/5). 20 × 18/5 = 72.
Explanation:
Power P = V²/R => R = V²/P = 200²/100 = 40000/100 = 400 Ω. Also current I = P/V = 0.5 A, R = V/I = 200/0.5 = 400 Ω. Use P = V²/R for direct calculation.
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