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)

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