# Two balls are thrown simultaneously A vertically upwards with a speed of 20m/s from the ground and B vertically downward from a height of 40 m with the same speed and along the same line of motion at what distance do the two balls collide? How to solve this question with the help of relative velocity}?

$lettheycollideatheightx\phantom{\rule{0ex}{0ex}}x=20t-\frac{g{t}^{2}}{2}\phantom{\rule{0ex}{0ex}}40-x=20t+\frac{g{t}^{2}}{2}\phantom{\rule{0ex}{0ex}}40-20t+\frac{g{t}^{2}}{2}=20t+\frac{g{t}^{2}}{2}\phantom{\rule{0ex}{0ex}}40-20t=20t\phantom{\rule{0ex}{0ex}}40t=40\phantom{\rule{0ex}{0ex}}t=1sec.\phantom{\rule{0ex}{0ex}}x=20-\frac{10}{2}=15m\phantom{\rule{0ex}{0ex}}\phantom{\rule{0ex}{0ex}}Regards$

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