I'm following an online physics course and I can't understand why for the question below the equation distance = speed $\times$ time can't be used while the equation $x_1 = x_0 + v_0t + 1/2at^2$ can. Could somebody please clarify why this is the case?
"A plane is moving at $30 \ m/s$. It accelerates at $2 \ m/s^2$ for $11$ seconds. How far does it travel during this time?"
Here's how I solved it which is wrong according to my book which uses the other equation.
I started by calculating the final velocity using $v_1 = v_0 + at$ which is $52 \ m/s$.
Using the final velocity I calculated the average velocity using $(v_1 - v_0) / 2$ resulting in $ 11 \ m/s$.
Inserting it into the equation $d = rt$ ($d = 11 \ m/s \times 11 \ s$) the answer is $121 \ m$.