# Can you allways use speed = distance /time relation

1. Oct 3, 2004

### Alem2000

My question is when you know your velocity and the distance traveled....can you allways use speed =distance /time relation to find time..? Because it seems to only work on some occasion...i know this sounds like a stupid question but i just dont get it. Or does your velocity have to be conastant to be able to use this relationship?

Last edited by a moderator: Mar 7, 2013
2. Oct 3, 2004

### robphy

displacement = velocity * time... only when velocity is constant.

3. Oct 4, 2004

### spacetime

time=dist./speed

even if the velocity is not constant, you can find the time taken.

Do the following.
Break up the whole motion into parts. And those parts should be such that the velocity is constant in them. Now, for each part, calculate the time as

(distance traveled in that part) / (speed in that part, which is constant)

so you see, now you can add up all of the time intervals to get the whole time.

If the numebr of intervals becomes way too large, then you need to use calculus.

spacetime
www.geocities.com/physics_all/index.html