Question

Two persons A and B start moving at the same time towards each other from points x and y, respectively. After crossing each other, A and B now take \( \frac{4}{6} \) hours and 6 hours, respectively, to reach their respective destinations. If the speed of A is 72 km/h, then the speed (in km/h) of B is:

• A. 54
• B. 56
• C. 60
• D. 64

Hint:

In relative motion problems, combine the speeds when objects move towards each other. Use the relationship between distances, speeds, and times to solve for the unknown quantities.

Answer 1

The Correct Option is C

Let the distance between A and B be \( D \). - The relative speed of A and B when they are moving towards each other is \( 72 + x \) (where \( x \) is the speed of B). - After crossing each other, the remaining distance is traveled at their individual speeds, i.e., \( \frac{D}{72 + x} \). We are given the time taken by both after crossing each other, and the relationship gives us the equation: \[ \text{Time taken by A} = \frac{D}{72}, \quad \text{Time taken by B} = \frac{D}{x} \] Using this relation, we can calculate the speed of B, which is 60 km/h. Thus, the speed of B is 60 km/h.