A ball is thrown upward with an initial velocity of 64 ft/sec from a height of 960 ft. It's height h, in feet, after t seconds is given by h(t)= -16t^2+64t + 960. After how long will the ball reach the ground? : When the ball strikes the ground, h(t) = 0, therefore -16t^2 + 64t + 960 = 0 ; Simplify & change the signs, divide thru by -16: t^2 - 4t - 60 = 0 :

Factor (t - 10)(t + 6) = 0 : Positive solution: t = 10 sec; The ball will reach the ground ; : Check solution in original equation h(t) = -16(10^2) + 64(10) + 960 h(t) = -1600 + 640 + 960 h(t) = 0; confirms our solution