# Free-fall acceleration problem

1. Feb 2, 2010

### bryans1mic

Problem states that a stone is thrown vertically downward with an initial
speed of 12.0 m/s from some tower.

well, i was wondering if i should use 12.0m/s or if i should use gravity (9.8 m/s)

will the rock have an initial speed of 12.0m/s then eventually become 9.8 m/s
or will it be 12.0 m/s until the rock hits the ground.

(all my book examples were throwing something upwards which is manageable but
going downward gots me stumped.)

thanks

2. Feb 2, 2010

### cepheid

Staff Emeritus
Hi bryans1mic, welcome to PF!

Be careful not to confuse velocity (m/s) with acceleration (m/s2). Objects in free fall (i.e. under the influence of gravity *only*) will accelerate downward at 9.8 m/s2. What this means is that although the object will start out with a velocity (initially) of 12.0 m/s downward, gravity will accelerate the stone so that its downward velocity increases (that's what acceleration is...the rate of change of velocity). Its velocity will increase by 9.8 m/s PER second. That's where the unit of m/s2 for acceleration comes from.