Two points A and B lie along a line at a distance of 120km apart. P and Q start at the same time from A and B with speeds 40km/h and 60km/h respectively. They travel towards each other and after their meeting for the first time, they then go in reverse directions and also interchange their speeds. These speeds are continued in their further journey. After reaching their respective starting points, they reverse their directions of travel and proceed towards each other again. The time taken by them to meet each other 2nd time is

First they go in opposite direction .

So, relative velocity of them is (40+60) km/h or 100 km/h.

So, time taken by them to meet for first time is =(120/100) h= 1.2 hours.

So,in their first meeting P travels =(1.2×40)=48 km and Q travels=(1.2×60)=72 km.

But,after first meeting P and Q reversed their speeds into 60 km/h and 40 km/h respectively.

Now,P will take (48/60)=0.8 hours to reach point A and Q will take (72/40)=1.8 hours to reach point B.

But in the mean time, P will move 60 km further from point A towards point B in next 1 hour when Q was traveling towards B.

So far ,after first meeting they traveled for 1.8 hours to get a head on move towards eachother.

So,for their second meeting they had to travel for only (120-60)=60 km.(as P already moved 60 km from point A)

So,100 km/h would be their relative velocity.

So,they will take (60/100)=0.6 hours to meet for the second time.

So,Total time taken by them to meet for the second time is=(1.2+1.8+0.6)=3.6 hours.

B is correct choice.