Finding the Speed of a Falling Ball with Constant Acceleration

[vivienwest]

Homework Statement

A small steel ball, dropped from rest, takes 0.5s to fall through a vertical distance of 1.25m.
Determine the actual speed of the ball when it has fallen through a vertical distance of 1.25m, assuming that acceleration is constant.

Homework Equations

v=s/t

The Attempt at a Solution

Long ago I was helped by a friend to get the result
( 1.25m x 2 ) / 0.5s = 5ms-1

but I've forgotten how did he come to that conclusion, and the reason behind (1.25mx2), help is much appreciated .

 

[Cyosis]

The formula [itex]s=vt[/itex] is only valid for constant speed. Does an object fall with constant speed?

Your friend used the following, correct equations:

1) [itex]s=\frac{1}{2}at^2+v_0t+x_0[/itex]
2) [itex]v=at+v_0[/itex]

These are valid for constant acceleration. You will need to combine both of them to get the answer.

 

[davieddy]

s = t*(u+v)/2