A man can row 8 km/h in still water. He takes 4 hours to row to a point and back when the current flows at 4 km/h. How far is the point? MCQ with Answer and Explanation
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Question #1
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A train 270 meters long is moving at a speed of 120 km/h. In how much time will it cross a man coming from the opposite direction at a speed of 15 km/h?
Correct Answer: Option C
Explanation:
Relative speed = 120 + 15 = 135 km/h = 135 * (5/18) = 37.5 m/s. Time = Distance / Speed = 270 / 37.5 = 7.2 seconds.
Relative speed = 120 + 15 = 135 km/h = 135 * (5/18) = 37.5 m/s. Time = Distance / Speed = 270 / 37.5 = 7.2 seconds.
This question belongs to:
Maths
Time Speed and Distance
Question #2
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A cross-country runner covers the sides of an equilateral triangular course at speeds of 8 km/h, 12 km/h and 24 km/h respectively. Find his average speed for the whole round.
Correct Answer: Option B
Explanation:
Let each side of the triangular course be 24 km. Total perimeter = 3 * 24 = 72 km. Total time taken = 24/8 + 24/12 + 24/24 = 3 + 2 + 1 = 6 hours. Average speed = 72 / 6 = 12 km/h.
Let each side of the triangular course be 24 km. Total perimeter = 3 * 24 = 72 km. Total time taken = 24/8 + 24/12 + 24/24 = 3 + 2 + 1 = 6 hours. Average speed = 72 / 6 = 12 km/h.
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Maths
Time Speed and Distance
Question #3
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A man can row 6 km/h in still water. If the speed of the current is 2 km/h, it takes him 3 hours to row to a place and back. How far is the place?
Correct Answer: Option C
Explanation:
Downstream speed = 6 + 2 = 8 km/h. Upstream speed = 6 - 2 = 4 km/h. Let distance be d. d/8 + d/4 = 3 => (d + 2d)/8 = 3 => 3d/8 = 3 => d = 8 km.
Downstream speed = 6 + 2 = 8 km/h. Upstream speed = 6 - 2 = 4 km/h. Let distance be d. d/8 + d/4 = 3 => (d + 2d)/8 = 3 => 3d/8 = 3 => d = 8 km.
This question belongs to:
Maths
Time Speed and Distance
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