from the third equation of motion
we know that--- \(v^2\) = \(u^2\)+2as ( where v= final velocity u= initial a= acceleration acting on body t= time s= distance covered)
when the body is thrown upward with initial velocity = u
its final velocity becomes zero when it reaches its highest point so v=0
acceleration acting on the body in the downward direction = -g m/s^2
\(0^2\)= \(u^2\)-2gs
s = \(\frac{u^2}{2g}\)
now it comes down so total distance = \(\frac{2u^2}{2g}\) (distance going up+distance coming down)
again it rebounds and goes upward with velocity = uf
total distance covered going up and coming down = \(\frac{2u^2f^2}{2g}\)
again it rebounds and goes upward with velocity = u\(f^2\) (we can find distance covered each time by above process)
this process continues till infinity
total distance covered during this process = \(\frac{2u^2}{2g}\)+\(\frac{2u^2f^2}{2g}\)+\(\frac{2u^2f^4}{2g}\)+............till infinity
total distance = \(\frac{u^2}{g}\)(1+\(f^2\)+\(f^4\)+\(f^6\)+............∞) (we see this forms geometric progression)
total distance = \(\frac{u^2}{g}\)(\(\frac{1}{1-f^2}\))....(sum of infinite GP with first term a and common ratio r is given by \(\frac{a}{1-r}\) when 0<r<1)
= \(\frac{u^2}{g(1-f^2)}\)