According to work-energy theorem, Initial K.E of cannon ball + Gravitational P.E = Total K.E at ground ⇒
1
2
mv12+mgh=
1
2
mv22 ⇒v12+2gh=v22⇒v22=v12+2gh Here, v1=initial‌speed=50m∕s h=height‌of‌cliff=55m So, v22=(50)2+(2×10×55) ⇒v22=2500+1100=3600 or v2=√3600=60m∕s.