Sky box or tombstone by rod wave

5.66 seconds from when the rock was thrown. first construct an expression to represent the distance from the water to the rock. first account for the starting distance. d = 43 + ? now add in the distance based upon the initial velocity d = 43 + 21t + ? now add in the acceleration due to gravity d = 43 + 21t - 0.5at^2 now substitute the known values into the formula. 5 = 43 + 21t - 0.5*9.8*t^2 subtract 5 from both sides and perform the multiplication 0 = 38 + 21t - 4.9t^2 we now have a quadratic function with a=-4.9, b=21, c=38. using the quadratic formula, we can find the solutions at t = 5.66 and t=-1.37 since the negative time doesn't make sense, the correct value will be t = 5.66 seconds.