# How to find velocity as a function of time?

1. Sep 4, 2008

### veronicak5678

1. The problem statement, all variables and given/known data

A ship with an initial velocity of 3 m/s moves toward a port 4km away. The ship's acceleration is a constant -0.1 cm/s^2.
What is the ship's velocity after 1 minute?
Will the ship stop before crahing into the port?

2. Relevant equations

v final = velocity initial +a delta t

2. Sep 4, 2008

### Hootenanny

Staff Emeritus
Welcome to PF veronicak5678,

You missed out one vital section:

3. Sep 4, 2008

### veronicak5678

attempt:

v final = 300 cm/s + -.01 cm/s^2

v final = 299.99 cm/s

4. Sep 4, 2008

### Hootenanny

Staff Emeritus
Notice that the acceleration is given in centimetres per second2, but you are asked for the velocity after one minute.

5. Sep 4, 2008

### veronicak5678

so the final velocity will be 299.4?

6. Sep 4, 2008

### Hootenanny

Staff Emeritus
Your method is correct, but there seems to be a typo in you're previous post:

7. Sep 5, 2008

### veronicak5678

Oops! I was rushing around yesterday. So I used v final = 300 cm/s + -.1 cm/s^2 (60 s) to get 294 cm/s. Is this correct for velocity after 1 minute? Seems to make sense...

I used (v final )^2 - (v initial)^2 = 2a(delta x), giving me 0-300 = 2 (-.1) delta x

so delta x = 1500. My units don't seem right, but i think this means it will stop at 1500 cm?

Last edited: Sep 5, 2008
8. Sep 5, 2008

### Kurdt

Staff Emeritus

Are you familiar with other kinematic equations?

https://www.physicsforums.com/showpost.php?p=905663&postcount=2

Think about what info you have, what you need and what equation will help you find it.

9. Sep 5, 2008

### veronicak5678

OK, using (v final )^2 = (v initial)^2 + 2a delta x, I get

300 + 2 (-.1) 400000 = v final ^2, so v final = 100. I think this means that at 400000 cm, the ship will still have a velocity of 100 cm/s, and will crash. Is that correct?

10. Sep 5, 2008

### Kurdt

Staff Emeritus
Yes that looks fine.

11. Sep 5, 2008

### veronicak5678

Cool. Thanks a lot for all your help!