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Question

Ankur jogs on a circular track X at $1 \frac{2}{3}$ m/s and Mahima jogs on track Y at $2 \frac{1}{12}$ m/s. The total length of Tracks X and Y is 0.325 km. Ankur makes 9 rounds of track X in the same time Mahima makes 5 rounds of track Y. The time taken (in seconds) by Mahima to complete one round of track X is:

The correct answer is
48

The problem asks for the time Mahima takes to complete one round of track X. We are given the speeds of Ankur and Mahima, the total length of their tracks, and the relationship between the number of rounds they complete in the same time.

Analyze Given Information

  • Ankur's speed, $v_A = 1 \frac{2}{3} \text{ m/s} = \frac{5}{3} \text{ m/s}$.
  • Mahima's speed, $v_M = 2 \frac{1}{12} \text{ m/s} = \frac{25}{12} \text{ m/s}$.
  • Total length of Track X and Track Y, $L_X + L_Y = 0.325 \text{ km} = 325 \text{ m}$.
  • Ankur completes 9 rounds of Track X in the same time Mahima completes 5 rounds of Track Y.

Calculate Track Lengths

Let $T$ be the time taken. The distance covered is Speed $\times$ Time.

  • Distance covered by Ankur in time $T$: $D_A = 9 \times L_X$. Time taken by Ankur: $T = \frac{9 \times L_X}{v_A}$.
  • Distance covered by Mahima in time $T$: $D_M = 5 \times L_Y$. Time taken by Mahima: $T = \frac{5 \times L_Y}{v_M}$.

Since the times are equal:

$ \frac{9 \times L_X}{v_A} = \frac{5 \times L_Y}{v_M} $

Substitute the speeds:

$ \frac{9 \times L_X}{\frac{5}{3}} = \frac{5 \times L_Y}{\frac{25}{12}} $ $ \frac{27 \times L_X}{5} = \frac{60 \times L_Y}{25} = \frac{12 \times L_Y}{5} $

This simplifies to:

$ 27 \times L_X = 12 \times L_Y $

Divide by 3:

$ 9 \times L_X = 4 \times L_Y $

We also know $L_X + L_Y = 325$. Express $L_Y$ in terms of $L_X$ from the ratio:

$ L_Y = \frac{9}{4} L_X $

Substitute this into the total length equation:

$ L_X + \frac{9}{4} L_X = 325 $ $ \frac{4 L_X + 9 L_X}{4} = 325 $ $ \frac{13 L_X}{4} = 325 $ $ L_X = \frac{325 \times 4}{13} = 25 \times 4 = 100 \text{ m} $

Now find $L_Y$:

$ L_Y = 325 - L_X = 325 - 100 = 225 \text{ m} $

Calculate Mahima's Time for Track X

We need to find the time taken by Mahima to complete one round of track X. This is given by:

$ T_{M, X} = \frac{\text{Length of Track X}}{\text{Mahima's Speed}} = \frac{L_X}{v_M} $

Substitute the values:

$ T_{M, X} = \frac{100 \text{ m}}{\frac{25}{12} \text{ m/s}} $ $ T_{M, X} = \frac{100 \times 12}{25} \text{ seconds} $ $ T_{M, X} = 4 \times 12 = 48 \text{ seconds} $
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Important Questions from Relative Speed

  1. Two places, A and B are 3710 kms from each other. A train leaves from A to B at the same time another train leaves B to A. The two trains meet at the end of 35 hours. If the train travelling from A to B travels 35 kmph faster than the other. Find the speed of the faster train. (In kmph)
  2. A truck, 1575 metres long is running at a speed of 109 km/hr. How many seconds will it take to cross a 1475 metres long train running in the same direction at a speed of 79 km/hr?
  3. A truck, 1600 metres long is running at a speed of 112 km/hr. How many seconds will it take to cross a 1500 metres long train running in the same direction at a speed of 82 km/hr?
  4. Two friends 10 km apart start running towards each other at speeds of 10 km/hr and 14 km/hr respectively. After how much time will they meet each other?
  5. Consider an equilateral triangle ABC as given in the following diagram :

     



     

    Two people start at the same time from points A and B with speeds 30 km per hour and 20 km per hour respectively, and move on the sides of the triangle in the clockwise direction. They meet each other for the first time at

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