Quadratic formula word problem: distance given by s=t^2-2t

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juliemariefort

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Hello there. I'm having trouble with this problem:

The distance traveled by an object moving in a straight line is given by s=t^2-2t, 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 15 feet (solve to the nearest tenth)?

I'm assuming I set the problem = 0? So, t^2-2t-s=0. From there I am stuck.
 
Re: Quadratic formula word problem

juliemariefort said:
Hello there. I'm having trouble with this problem:

The distance traveled by an object moving in a straight line is given by s=t^2-2t, 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 15 feet (solve to the nearest tenth)?

I'm assuming I set the problem = 0? <-----No. s is the distance...the distance is to be 15
So, t^2-2t-s=0. From there I am stuck.
Click to expand...

Since you want to know when the distance is 15 feet, substitute 15 for s:

15 = t^2 - 2t

Now, get one side equal to 0:

0 = t^2 - 2t - 15

And solve...you may be able to factor, or you may wish to use the quadratic formula.
 
juliemariefort said:
… it will take 5 seconds to move 15 feet?
Click to expand...


Do you know? You can check your own answer.

If you want to know whether or not a value of t = 5 results in a value of s = 15, then substitute t = 5 into the formula for s and evaluate.

s = (5)^2 - 2(5)

If this evaluates to s = 15, then your answer is correct.

 
I was just wondering about the answer because the original question requested to "solve to the nearest tenth." I didn't expect the answer to work out to a whole number.
 
juliemariefort said:
I was just wondering about the answer because the original question requested to "solve to the nearest tenth." I didn't expect the answer to work out to a whole number.
Click to expand...


Then that is the question that you should have asked.

The answer could be written as 5.0 seconds, if you would like to show explicitly that the nearest tenth is zero tenths. This is always implicit when writing a natural number.

 
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