Answer:
[tex]initial velocity=19 ms^{-1}[/tex]
greatest height=48.05 m
Explanation:
Applying motion equations,
upward motion (g= -10m/s2)
where
u = initial velocity
v = final velocity
g = gravitational acceleration
s = distance
[tex]v^{2}=u^{2} +2gs\\31^{2} = u^{2}+2*(-10)*(-30)\\u^{2}=361\\u=19 ms^{-1}[/tex]
2)when the rock is at the highest point the velocity = 0
[tex]v^{2}=u^{2} +2gs\\0=361-2*10*S\\S=18.05 m[/tex]
total high to the highest point = 18.05 +30
= 48.05 m
