How do I find the final velocity and how high the bridge is?

[Julia Smith]

Homework Statement

A rock that is thrown upward from a bridge with an initial velocity of 2.0 m/s. (Assume there is no air drag: a = -10m/s²).
a) If the rock takes 4.0 s to hit the water below once the rock is released. What is the final velocity of the rock as it hits the water?
b) How high is the bridge?

Homework Equations

v = u +at
x = x₀ + v_it + 1/2*a*t²

The Attempt at a Solution

For (a), I know that the equation I can use is v = u + at. u being initial velocity.
v = (2.0m/s) + (-10m/s²) (4.0s)
v = -38 m/s
However, for (b), I do not know how I can solve it and need help on that ASAP

 

[haruspex]

for (b), I do not know how I can solve it

Your second relevant equation looks useful.

 

[NascentOxygen]

Hi Julia Smith.

Your equation is right if x is displacement, so just treat x_o as zero.

I'd prefer the equation be written using s for displacement, viz.,
s = ut + ½at²

where s is the displacement due to this acceleration.
You can throw in a term s_o if you wish, but it seems an unnecessary complication.