M2 AQA - work energy and power

I'm looking at question 6 in the pdf below.

I've managed to get the answer in the book but I want to know why, for part b, does the question use the word just.

I'm posting my workings too in case I've managed to get the answer by fluke without accounting for the just bit.

Can't follow the reasoning for your working.

To just get round the circle all the KE when the mass is projected will be converted to GPE at the top of the circle, and the speed would be zero at the top. The question is poorly worded as the initial velocity would have to exceed this value to get all the way round, i.e. continue from the top. Hence we look for the minimum speed where it supposedly just goes round.

So, gain in GPE = loss in KE

And $\frac{1}{2}mu^2=mga$

and solve.