Two trains 150m and 170m long are running towards each other on parallel tracks at speeds of 42 km/h and 30 km/h respectively. In what time will they clear each other? MCQ with Answer and Explanation
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Question #1
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A motorboat covers 12 km upstream and returns back to the starting jetty in 3 hours. If the speed of the boat in still water is 9 km/h, find the speed of the river current.
Correct Answer: Option D
Explanation:
Let the speed of the current be c km/h. 12 / (9 - c) + 12 / (9 + c) = 3. Dividing by 3: 4 / (9 - c) + 4 / (9 + c) = 1 => 4(9 + c + 9 - c) = 81 - c^2 => 72 = 81 - c^2 => c^2 = 9 => c = 3 km/h.
Let the speed of the current be c km/h. 12 / (9 - c) + 12 / (9 + c) = 3. Dividing by 3: 4 / (9 - c) + 4 / (9 + c) = 1 => 4(9 + c + 9 - c) = 81 - c^2 => 72 = 81 - c^2 => c^2 = 9 => c = 3 km/h.
This question belongs to:
Maths
Time Speed and Distance
Question #2
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A standard boat can row 12 km/h in still water. If the speed of the current is 2 km/h, find the time required to log 30 km upstream.
Correct Answer: Option A
Explanation:
Upstream speed = 12 - 2 = 10 km/h. Time required = Distance / Upstream speed = 30 / 10 = 3 hours.
Upstream speed = 12 - 2 = 10 km/h. Time required = Distance / Upstream speed = 30 / 10 = 3 hours.
This question belongs to:
Maths
Time Speed and Distance
Question #3
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A bus runs at 40 km/h for 2 hours and 50 km/h for the next 3 hours. Find the average speed of the bus for the total journey.
Correct Answer: Option D
Explanation:
Distance 1 = 40 * 2 = 80 km. Distance 2 = 50 * 3 = 150 km. Total distance = 230 km. Total time = 2 + 3 = 5 hours. Average speed = 230 / 5 = 46 km/h.
Distance 1 = 40 * 2 = 80 km. Distance 2 = 50 * 3 = 150 km. Total distance = 230 km. Total time = 2 + 3 = 5 hours. Average speed = 230 / 5 = 46 km/h.
This question belongs to:
Maths
Time Speed and Distance
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