IIT JEE , AIEEE Forum - Physics , Mechanics

rooney

Let velocity of car A be V.
So, total distance of path is 120V (since time taken to reach Y is 120min).

Let us assume for our convenience that the car leaves X JUST AS a car arrives at X from Y.

Now, relative velocity of Car A and the next car coming from Y is 2v. And the distance between A and the next car is 10V (since each car from Y leaves in every 10 min). So, A meets the next car at t = 10V/2V = 5 min.

So, it keeps meeting a car at every 5 min. So in 120 min, it meets 120/5 = 24 cars.

The last car is the one which is just leaving as A reaches Y. So, we dont count that (just like we didnt count the car reaching X when A was leaving X).

So , final answer is 24 - 1 = 23.

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