A locomotive 180 meters long crosses a modern bridge in 30 seconds. If it takes 12 seconds to pass a single post light, find the length of the bridge. MCQ with Answer and Explanation

Explanation:
Downstream speed = 48 / 4 = 12 km/h. Upstream speed = 24 / 4 = 6 km/h. Speed in still water = (Downstream speed + Upstream speed) / 2 = (12 + 6) / 2 = 9 km/h.

Explanation:
Let the required speed for the second half be x km/h. Using the average speed formula for equal halves: Average Speed = 2v1*v2 / (v1 + v2) => 50 = (2 * 40 * x) / (40 + x) => 50(40 + x) = 80x => 2000 + 50x = 80x => 30x = 2000 => x = 66.67 km/h.

Explanation:
New speed = 5/7 of usual speed => New time = 7/5 of usual time. Difference = 2/5 of usual time = 12 minutes. 1/5 of usual time = 6 minutes => Usual time = 6 * 5 = 30 minutes.