Hey, i have the mark scheme for this question but i simply do not understand it.the question is here :

maths problem , part E . the answer is here:

answer .

I don't understand, what i did was use equations of motion , from the point when Q reverses and falls 3.15 m, therefore giving me the value of V from v^=u^2+2as

v^2=0+2x(9.8x3.15)

this is wrong. the above equation is true for a particle in free fall. P is not in a free fall
v=7.857 m/2

so i used V=U+at

giving t=0.8017

What is wrong with my method? Would appreciate help, been bugging me all day