During the "May Day" period, two groups of tourists from Changchun took buses and cars along the same route to Dalian, as shown in the figure.

(1) Let the functional relationship between bus distance and time be y 1=k 1x, and the relationship between bus distance and time be y2=k2x+b2, which is obtained from the image.

200=5k 1, the solution is: k 1=40,

0=2k2+b2200=4k2+b2，

Solution: K2 = 100b2 =? 200,

Then y 1=40x, y2= 100x-200,

Therefore, the functional relationship between bus distance and time is y 1=40x, and the relationship between bus distance and time is y2 =100x-200.

(2) From the meaning of the question, you can get

The speed of the bus is: 200÷5=40km/ h,

Vehicle speed: 200÷(4-2)= 100km/ h 。

③ When y 1=y2,

40x= 100x-200，

Solution: x=3 13,

Then 3 13-2 = 1 13.

So the bus caught up with the bus 1 13 hours after departure.