Constant acceleration equations (SUVAT)

[sharbie]

Homework Statement

A stone is projected horizontally from the top of a vertical sea cliff 49m high, with a speed of 20ms^-1. Neglecting air resistance, calculate:
The time that it takes to reach the sea.

Homework Equations

v² =u²+2as
t=v-u/a
t=d/s

The Attempt at a Solution

I'm not sure whether i should be calculating v-final velocity via v² =u²+2as and using that to find t, ie. t=v-u/a
or simply
t=d/s

can anybody enlighten me please? thanks

 

[sharbie]

sorry about the layout by the way, don't know what happened there- first time user anyway, would much appreciate help please

 

[p21bass]

The only thing you're concerned with (for the problem, as stated) is the time it takes to drop vertically. And, since it's projected horizontally, it doesn't matter what the initial velocity is. Hint: v_0y = 0.

You need to use the constant-acceleration equation that relates initial position, final position, acceleration, time, and initial velocity (0 m/s).EDIT: You don't need (for this problem) to find out the final velocity.