# Homework Help: Acceleration formula help

1. Jun 19, 2006

### Genowyn

OK. I am doing my science summative and have entirely forgotten what formula to use to find how long it takes something to travel a certain distance, given the acceleration.

More specifically, I need to know the formula for how long it takes something to fall 125m to the ground.

Also, how do I find velocity if the start position of my object is the same as the first one. (I know the speed, just not the direction.)

Last edited: Jun 19, 2006
2. Jun 19, 2006

### dav2008

3. Jun 19, 2006

### Genowyn

All of the ones on that page seem to require that I know the final velocity. I don't know the final velocity, just the distance, initial velocity, and acceleration.

So, I still have no idea what to do.

4. Jun 19, 2006

### dav2008

You can use equation 4 to solve for the final velocity and then use equation 3 to solve for the time.

5. Jun 19, 2006

### Genowyn

I see, thank you.

Does anyone know about how I find direction if the start and end point are the same point?

6. Jun 19, 2006

### NEWO

The displacement is zero, hence no direction, i think that is right judging from what your question is asking

7. Jun 19, 2006

### Genowyn

So the velocity is just the same as the speed?

8. Jun 19, 2006

### lightgrav

No.
Average speed is the total path distance traveled divided by the time taken
(there and back again distances adding up)
Average velocity is the "net" displacement (zero, here) divided by time.

Their "complete set of formulas" is missing 3b : Dx = v_f t - 1/2 a t^2 .