How Do You Calculate Distance When Velocity Changes?

[bigzee20]

Homework Statement

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

 

[heth]

Homework Statement

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

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

 

[bigzee20]

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

 

[heth]

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

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.

 

[bigzee20]

Iam still confused lol

 

[heth]

Iam still confused lol

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.)

 

[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

 

[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.