A baseball is thrown upward from ground level at an initial velocity of 64 feet per second. After t seconds, it's height is given by the formula h=-16^2+64t. After how many seconds will it be 48 feet?

Solution:

      h=-16t^2+64t

      h=-16t^2+64t = 48

       16t^2 - 64t + 48 = 0

           t^2 - 4t + 3 = 0

          (t - 1)(t - 3) = 0

          t = 1  or  t = 3

   Here answer will be 1 sec for upward motion.