A boat crew rows 30 km upstream and 50 km downstream, taking exactly 5 hours for each independent passage. Find the speed of the current stream. MCQ with Answer and Explanation
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Question #1
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A car travels a distance of 360 km at a uniform speed. If the speed is reduced by 10 km/h, it takes 2 hours longer. Find the original speed.
Correct Answer: Option B
Explanation:
Let original speed be s. 360 / (s - 10) - 360 / s = 2 => 180 / (s - 10) - 180 / s = 1 => 180(10) = s(s - 10) => 1800 = s(s - 10). Solving s^2 - 10s - 1800 = 0 gives (s - 45)(s + 40) = 0. Since speed is positive, s = 45 km/h.
Let original speed be s. 360 / (s - 10) - 360 / s = 2 => 180 / (s - 10) - 180 / s = 1 => 180(10) = s(s - 10) => 1800 = s(s - 10). Solving s^2 - 10s - 1800 = 0 gives (s - 45)(s + 40) = 0. Since speed is positive, s = 45 km/h.
This question belongs to:
Maths
Time Speed and Distance
Question #2
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A car travels the first half of a total distance at speed v1 and the second half at speed v2. What is the expression for the average speed of the car?
Correct Answer: Option B
Explanation:
When equal distances are traveled at speeds v1 and v2, the average speed is the harmonic mean: 2v1*v2 / (v1 + v2).
When equal distances are traveled at speeds v1 and v2, the average speed is the harmonic mean: 2v1*v2 / (v1 + v2).
This question belongs to:
Maths
Time Speed and Distance
Question #3
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A train 150 meters long completely passes a stone in 15 seconds. Find the speed of the train in km/h.
Correct Answer: Option C
Explanation:
Speed of train = 150 / 15 = 10 m/s. In km/h = 10 * (18/5) = 36 km/h.
Speed of train = 150 / 15 = 10 m/s. In km/h = 10 * (18/5) = 36 km/h.
This question belongs to:
Maths
Time Speed and Distance
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