Distance between a boat and a dock problem : A boat is tied to a dock by means of a cable 60m long. if the dock is 20 m above the water and if the cable is being drawn in the rate 10m/min, express the distance y m of the boat from the dock after t min. I saw this problem in the first pages of a math book which was about functions. i know the answer notwithstanding i still can`t understand why ??? the answer is : $10\sqrt{t^2-12t+32}$ can any one help me to solve it (:

Yes you right, the question is really simple I thought that the cable is moving toward the water like a parabola but actually it is being drawn by someone on the dock

$\sqrt{(60-(t*10))^2 - 20^2}$ = $\sqrt{3600+100t^2-1200t-400 }$ =$10\sqrt{t^2-12t+32}$