Multiple choice

The total distance covered by a car is 200 m. It covers the first half of the distance at a speed of 40 kmhr-1 and the second half of distance at speed v. If its average speed is 48 kmhr-1, the value of v is: [NTSE - Stage - 1, 2017-18, Tamil Nadu]

  1. 52 kmhr-1

  2. 60 kmhr-1

  3. 48 kmhr-1

  4. 65 kmhr-1
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B Correct answer
Explanation

Average speed = 2 * v1 * v2 / (v1 + v2). 48 = 2 * 40 * v / (40 + v). 48 = 80v / (40 + v). 48(40 + v) = 80v. 1920 + 48v = 80v. 32v = 1920. v = 60.

AI explanation

When equal distances are traveled at different speeds, the average speed equals twice the product of the speeds divided by their sum, which gives the equation 48 equals 2 multiplied by 40 multiplied by v divided by 40 plus v. Simplifying this, 48 multiplied by 40 plus v equals 80v, so 1920 plus 48v equals 80v. Solving for v gives 32v equals 1920, so v is 60 km/hr. The value of v is 60 km/hr.

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