EXAMPLE 3 Suppose that a ball is dropped from the upper observations deck of the CN Tower in Toronto, 450 m above the ground. Find the velocity of the ball after 3 seconds. SOLUTION Through experiments carried out four centuries ago, Galileo discovered that the distance fallen by any freely falling body is proportional to the square of the time it has been falling. (This model for free fall neglects air resistance.) If the distance fallen after t seconds is denoted by s(t) and measured in meters, then Galileo's law is expressed by the equation s(t) = 4.9t2