# Distance and displacement of an object on a straight line [closed]

I had this homework problem, but don't actually know if what I did is right, or that I even read the problem correctly. Can someone please tell me if this is the right interpretation of the problem and my answer is right or wrong?

1. at $t=0s$ an object has a position of $-4.0m$ and without changing direction moves to a position of $+6.0m$ at $t=4.0s$ It then moves in a straight line and accomplishes a displacement of $-8.0m$ at the $t=8.0s$ mark. For the $8.0s$ interval:

a. What was the total distance the object traveled?
b. What was the objects overall displacement?
c. What has been the object's average speed?
d. What has been the objects average velocity?
e. At $t=8.0s$, what is the object position?

So what I did is this:

a. I did $6-(-4)-(-8)$ and got a total distance of $22m$

b. It says the displacement of $-8.0$m

c. Average speed would be $\frac{22m}{8.0s}=2.75m/s$

d. Average velocity would be $\frac{-8.0m}{8.0s} = -1.0m/s$

e. Would it be $-12.0m$?

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## closed as too localized by Qmechanic♦, dmckee♦Sep 13 '12 at 21:07

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Welcome to Physics Stack Exchange, Link! I completely forgot until now to let you know that "check my work" questions are not really encouraged on this site, and that's why your question got closed. If you have a particular reason to believe that something you did might be wrong, e.g. an answer doesn't make sense, or there is a concept that you're not sure how to apply, then make the question about that, and it can be a great question. See our homework policy and FAQ for more information. –  David Z Sep 13 '12 at 23:57
Okay then, thanks, I didn't know, I'll keep that in mind for next time. –  Link Sep 14 '12 at 0:41

Suppose that the object was traveling on x-axis, hence we have following $(@t = 0,\ x = -4);\ (@t = 4,\ x = 6);\ (@t = 8,\ x = 6-8 = -2)$ Hence we have

$a)\ \ {{|(6 - (-4))| + |(-2 - 6)|}} = 18.$

$b)\ \ {-2 - (-4)} = 2.$

$c)\ \ {18\over8}.$

$d)\ \ {2\over8}.$

$e)\ \ -2.$

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Ahh, that makes sense, thanks, never thought of it that way. –  Link Sep 13 '12 at 20:51
quartz, our homework policy specifies that we shouldn't post complete answers to homework-like questions like this. Normally I would temporarily delete this, but since it has already been read and accepted I'll leave it alone. Just keep this in mind in the future. –  David Z Sep 13 '12 at 21:29
Yea, this is fine, but I would have liked pointers, but nice job, especially like the sentence about the x-axis, once i got that, everything else was cake. –  Link Sep 13 '12 at 21:39