In one of physics problem in my worksheets, I used quadratic formula to find the time and I got two positive values. How can I figure which one is true?

Question

mayankdevnani · Answer

http://www.helpalgebra.com/articles/quadraticequations.htm

mayankdevnani · Answer

go through...          @micahwood50

anonymous · Answer

Thanks, but I know how to use quadratic formula. I just got two positive values for time and I don't know which one is true...

mayankdevnani · Answer

which?

anonymous · Answer

which time is true? How can I do that?

mayankdevnani · Answer

it was hint http://www.purplemath.com/modules/solvquad4.htm

anonymous · Answer

Saying, I got t = 10s and 30s. How can I tell which one is true? I mean I can't use both of them in physics.

mayankdevnani · Answer

in my view, 30s is appropriate answer and because generally time is usually come in quadratic formula........ok

anonymous · Answer

What do you mean? I have two values...

mayankdevnani · Answer

30s

anonymous · Answer

Why?

anonymous · Answer

Can you prove it?

ash2326 · Answer

@mayankdevnani it depends on the question, also for some questions both may be correct.
Like here find the time at which the body is at height say h
This is for a projectile|dw:1348570318599:dw|, it'll cross that height two times, so we'll get two times both are correct.

mayankdevnani · Answer

@ash2326        m guessing it,.......

ash2326 · Answer

sorry mentioned the wrong person
@micahwood50 the post was for you

anonymous · Answer

And if the height is the maximum height?

ash2326 · Answer

then there would be obviously one time

anonymous · Answer

Well, I got two positive values of time for this. How can I tell which one is true?

ash2326 · Answer

Find acceleration at both the times, you'll get acceleration 0 for one of the two times, that one is your answer.

ash2326 · Answer

I'm inquisitive to know the question, could you post it here?

anonymous · Answer

Well, in problem in processing, I got t = 10.553s and 0.051s. I know it's 10 because another one is too small to be true, though. I'm asking, just in case I face something like that in the future.

anonymous · Answer

Still want to see my problem?

ash2326 · Answer

it's ok, check acceleration value, if it's zero for a time, then that is our answer

anonymous · Answer

Ok, thanks. Do you want me to post the question?

ash2326 · Answer

No, it's fine
Thanks

anonymous · Answer

A projectile is fired into the air from the top of a 200-m cliff above a valley. Its initial velocity is 60 m/s at 60º above the horizontal. Where does the projectile land?

anonymous · Answer

I just have to find the time to find the range.

ash2326 · Answer

you would have got t=10 seconds and range=519.61 meters
haven't you?

anonymous · Answer

Actually, I got range = 406 m