# Acceleration and velocity

1. Oct 22, 2008

### bigzee20

1. The problem statement, all variables and given/known data
A plane is moving at 270 m/s accelerates at 28 m/s ^2 for 9.8s. How far would it have traveled in the time.

using vi + a(t) i was able to get its final velocity 544.4m/s but when i multiply it by 9.8s it tells me that is wrong what am i doing wrong? thanks

2. Oct 22, 2008

### heth

For what length of time does the plane travel at a speed of 544.4 m/s?

3. Oct 22, 2008

### bigzee20

9.8s but when i multiply it by 544.4 m /s its wrong??

4. Oct 22, 2008

### heth

What speed did the plane have at the start of the 9.8s? Try doing a before and after sketch with the plane's speed labelled each time.

5. Oct 22, 2008

### bigzee20

Iam still confused lol

6. Oct 22, 2008

### heth

a. What speed was the plane going at right at the start of the question?

b. What speed was the plane going at right at the end of the question, 9.8 s later?

c. What do you think it was doing in between :-)

(Once you've got that conceptually, you can start to think about distance. If you just plug and chug with an equation for the distance right now, you'll be confused about a lot of things later in your course.)

7. Oct 22, 2008

### bigzee20

I got it man !!!!! woot.
Here it is d = Vi(t)+1/2a(t)^2
therefore 270(9.8) + 1/2(28)(9.8)^2
= 3990.56 m
THANKS heth

8. Oct 23, 2008

### heth

Nice one! The key is realising that the plane's velocity is changing all the time, so you can't use an equation that assumes the velocity is constant.