
Distance covered by ball A is h=50(2)−21×10×22=100−20=80m
Now, at time t=2s, velocity of A is vA=50−10×2=30ms−1
Relative velocity of both balls after 2s is vrel=50−30=20ms−1
Here, relative displacement xrel=80ms−1 and relative accelerationarel=0.
Time taken t=2080=4s
Time at which they will meet is t=4+2=6s