Simple problem that webassign keeps saying wrong

  • Thread starter xX1SHOt
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In summary, the average speed of a nitrogen molecule in air is about 670 m/s, and its mass is about (4.68 x 10^-26)kg.
  • #1
xX1SHOt
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1. Homework Statement

The average speed of a nitrogen molecule in air is about 670 m/s, and its mass is about (4.68 x 10^-26)kg.

(a) If it takes (3.60 x 10^-13)s for a nitrogen molecule to hit a wall and rebound with the same speed but moving in an opposite direction (assumed to be the negative direction), what is the average acceleration of the molecule during this time interval?
____________ m/s^2

(b) What average force does the molecule exert on the wall?
____________N


2. Homework Equations

Ok, here is the basic kinematic equation and force equation. I used both of these equations to talk to my professor after class 2 days ago to solve it and he got the same answer. I emailed him today and he said you use the average acceleration kinematic equation to solve it but that's what we did, i don't know if he doesn't remember or there is some secret one that i have never been informed of.

a)- (final velocity - initial velocity) / (change in time) = average acceleration

b)- (mass * average acceleration) / (change in time) = average force


3. The Attempt at a Solution

a) (-670-670) / (3.6 x 10^-13) = approximately (-3.722 x 10^15)m/s^2
Webassign's response: "Answer has wrong sign"
My next answer: ([positive now]3.722 x 10^15)m/s^2
Webassign's response: "Answer has wrong sign"
Advice on tricky wording or problem or something?

b) [(3.722 x 10^15)*(4.68 x 10^-26)] / (3.6 x 10^-13) = 483.86 N
Webassign's response: "Answer is off by an order of magnitude"
My next answer: -483.86 N
Webassign's response: "Answer has the wrong sign"

Honestly this makes no sense but if anyone can help or gets a different answer you help would be greatly appreciated
 
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  • #2
For part a) I don't really see what's wrong either other then I got exactly -3.725 instead of your -3.722 but you noted it was approximate. For part b), you don't divide by the time interval. F = ma, and averages can take the place of instantaneous F, a. Remember to check your dimensions, your computation has units of kg*m/s^3 which is not a unit of Force.
 
  • #3
Excellent point about b) i can't believe that i missed that one thank you very much. But you are saying that there is no explanation for a being wrong. and the .003 off shouldn't matter because as long as you are within 1% or the correct answer it will give it to me.

EDIT: Your help has been great can you look at my other problem as well:
https://www.physicsforums.com/showthread.php?p=2237013#post2237013
 
Last edited:

1. Why does webassign keep saying my answer is wrong?

Webassign uses an algorithm to check your answers, so it may not recognize alternative ways of expressing the solution. Double-check that you are using the correct units and that your answer is in the correct format.

2. Can I get partial credit if my answer is almost correct?

Webassign does not give partial credit, so it is important to use the exact format and units specified in the problem. However, if you are consistently getting answers that are close but not quite right, it may be helpful to review the concepts and practice more problems.

3. Is there a way to check my work before submitting my answer?

Yes, webassign often provides a "Check Answer" button that will show you if your answer is correct or incorrect. This can help catch any simple mistakes before submitting your final answer.

4. What should I do if my answer is still marked wrong, even after checking my work?

If you are confident that your answer is correct and it is still marked wrong, you can try reaching out to your instructor for clarification. They may be able to provide insight on the specific format or approach that webassign is expecting for that problem.

5. Can I use a calculator on webassign?

Webassign provides a built-in calculator for some problems, but it is always a good idea to check the instructions for the specific problem to see if calculators are allowed. For some problems, you may be expected to show your work without the use of a calculator.

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