Intermediate Algebra: Find time to move 19 feet, given....

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Helen

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The position of an object moving in a straight line is given by s(t) = t^(2) - 8t where s is in feet and t is the time in seconds
the object has been in motion. How long will it take the object to move 19 ft?

Could someone show me how to put this together?
 
Re: Intermediate Algebra

Helen said:
The position of an object moving in a straight line is given by s(t) = t^(2) - 8t where s is in feet and t is the time in seconds the object has been in motion. How long will it take the object to move 19 ft? Could someone show me how to put this together?
Click to expand...
You're given the equation....AND the distance. Substitute 19 for s(t):

19 = t[sup:1x71iqpk]2[/sup:1x71iqpk] - 8t

Now...solve the equation, which is very much like the previous equations you've been posting.
 
Re: Intermediate Algebra

This is a very bad question. I can think of at least two ways to answer it.

1) When does the object get to s = 19' (It doesn't actually say this, but it may be what is intended. I'm hoping this is NOT what it means, but if you do it the other way and it gets marked wrong, I would have a very sincere discussion with the teacher or grader.)

s(t) = t^2 - 8t = 19' ==> t = 9.916 sec

2) How long does it take to travel 19'.

Since it starts out moving backwards, we have to find out how far back it moved. Then, we must travel that distance back to s = 0'. and travel the rest so whereever the total trip measured 19'.

Using the usual treatment of parabolas, we see that the maximum negative displacement is t = -b/(2a) = 8/(2*1) = 4 sec. This suggests that s(4 sec) = -16' is the maximum negative displacement. This leaves us only 3' left to travel!

So, solve s(t) = t = -13' ==> Two solutions, t = 5.732 sec and 2.268 sec. We need the one greater than t = 4 sec, so t = 5.732 sec is the answer, having moved 16' back and 3' forward.
 
Re: Intermediate Algebra

tkhunny, Thank you for the help.
What would be the other way? Helen
 
Re: Intermediate Algebra

mrspi,
Do I rearrange the equation?
example: 19 + t^ (2) - 8t =0
Thank you, Helen
 
Re: Intermediate Algebra

Helen said:
mrspi,
Do I rearrange the equation?
example: 19 + t^ (2) - 8t =0
Thank you, Helen
Click to expand...

Helen, please follow TKHunny's recommendations...his response is much more appropriate than mine. I made a bad assumption....
 
Re: Intermediate Algebra

Helen said:
tkhunny, Thank you for the help.
What would be the other way? Helen
Click to expand...
The ways are numbered 1) and 2)
 
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