For b) I was curious why i couldn't use $s = ut + \frac12at^2$ as my equation as i had all the necessary known values. Instead to get the correct answer i had to use $v=u + at$.

Why do you think you cannot use $s=ut+\frac12 at^2$? As you state, you have the necessary values of $s, u, a$. There is only one unknown variable $t$. You will need to solve a quadratic equation, but it is not impossible.

It is much simpler to use $v=u+at$. But this does not prevent you from using any other formula.

It is much simpler to use $v=u+at$. But this does not prevent you from using any other formula.

edited Jan 7 by sammy gerbil