Further, Mathematica solves the equation with the following code

Input := 


t[d_]=Sqrt[d/4.9];

Input := 


distance=d/.Solve[eq1, d][[1]]

Output =


385.249

Input := 


timedown=t[distance]//N

Output =


8.86692

Input := 


timeup=distance/340//N

Output =


1.13308