Answer:
rock A: [tex]y=90-1/2*g*t^2[/tex]
rock B: [tex]y=30*t-1/2*g*t^2[/tex]
g=9.81m/s^2
Explanation:
Kinematics equation:
[tex]y=y_{o}+v_{oy}*t+1/2*a*t^2[/tex]
in our case the acceleration is the gravity and it has a negative direction.
a=-g
rock A, yo=90m, Voy=0m/s:
[tex]y=90-1/2*g*t^2[/tex]
rock B, yo=0m, Voy=30m/s:
[tex]y=30*t-1/2*g*t^2[/tex]