1. The problem statement, all variables and given/known data A jet plane comes in for a landing with a speed of 100 m/s, and its acceleration can have a maximum magnitude of 5.00 m/s^2 as it comes to rest. (a) From the instant the plane touches the runway, what is the minimum time interval needed before it can come to rest? 2. Relevant equations Kinematics I suppose, but I'm trying to solve it with just calculus. 3. The attempt at a solution So my idea was that if the acceleration is constant at -5m/s^2 then I should be able to take the integral of this and get the velocity function. So what I end up with is v(t) = - 5/2 (t^2) + 100 Solve for v(t) = 0 etc. But the answer is wrong. It's supposed to be 20s. Where is my logic flawed?