Two cars are moving in the same direction with the same speed 30 km/hr.They are separated by a distance of 5 km. What is the speed of a car moving in the opposite direction if it meets these two cars at an interval of 4 minute?


Correct option is

45 km/hr


As the two cars (say A and B) are moving with same velocity the

relative velocity of one (say B) with respect to the other, A,


So, the relative separation between them (= 5 km) always remains the same.

Now if the velocity of the car (say C), moving in opposite direction to Aand B is  relative to ground, then the velocity of car C relative to A andB will be


But as  is opposite to vC


So, the time taken by it to cross the cars and B,


or                        vC = 45 km/h



A person walks up a stalled escalator in 90 second. When standing on the same escalator, now moving he is carried up in 60 second. How much time would it take him to walk up the moving escalator?