Calculating height in free falling problems

[akalei]

Homework Statement

A student stands at the edge of a vertical cliff and throws a stone vertically upwards. The stone leaves the student's hand with a speed of v=8.0m/s, the acceleration of free fall is 10m/s² and all distance measurements are taken from the point where the stone leaves the student's hand. Ignoring air resistance calculate the time taken by the stone to reach its maximum height.

The time between the stone's leaving Antionio's hand and hitting the sea is 3.0s. Determine the height of the cliff.

Homework Equations

unknown

The Attempt at a Solution

s= ut + 1/2at²
s= (8)(3) + 1/2(10)(3)²
s= 69

 

[PhanthomJay]

If you take positive as up, then negative is down. Which way does vo (u) act? Which way does the acceleration act? Which way is the displacement of the stone to the sea? Don't forget part a.

 

[akalei]

i think i understand what your saying but i don't understand how to use the information to solve the problem

 

[PhanthomJay]

For the equation you wrote for displacement, you have a signage error in one of the terms on the right side of the equation. Can you spot it??