Two airplanes depart at the same time from Paris to London. One flies with a velocity of 350 km/h and the other flies with v=280 km/h. After 2 hours, the first airplane decreases its velocity with 230 km/h. At what distance from Paris does the second plane reach the first airplane?
I found after two hours that the first airplane will have done 700 km and the second will have done 560 km/h. But from then, I don't understand how we can connect the dots.
Firstly, your tags are incorrect - there are no links to calculus or derivatives in this problem.
After the 2 hours:
Plane 1 distance = 700 km Plane 1 Velocity = 230 km/h
Plane 2 distance = 560 Plane 2 velocity = 280 km/h
For each hour, Plane 2 gains (280 - 230 = 50km) on Plane 1
So
Time to match Plane 1 d/s = (700-560)/50 = 2.8 hours
Therefore
distance = t x s = 2.8 x 230 = 644
644 + 700 = 1344 km from Paris (and you can check this by doing 560 + (2.8 x 280))
Hope that helps!