Two airplanes land simultaneously at opposite ends of a narr

Two airplanes land simultaneously at opposite ends of a narrow runway, a distance
D = 1250 m apart. The two planes touch down with speeds v1 = 65.0 m/s and v2 = 75.0 m/s, and each
brakes with the same constant deceleration a = -4.00 m/s2. (a) Do they stop before they crash into one
another? (b) If so, how far apart are they when they both have stopped? If not, what is their relative
velocity when they crash?

Solution

Distance traveeld by airplane 1 when its final speed become zero at stop, is s₁

v₁² = u₁² - 2as₁

s₁=u₁² /2a = (65)2/2x4 = 528.125 meter

Similarly for airplane 2 is s₂

s₂=u₂² /2a = (275)2/2x4 = 703.125 meter

s₁ + s₂ = 1231.25, which is less than 1250, the initial distance between airplanes, so they will not crash, and they are 1250 - 1231.25 = 18.75 meter apart.