Physics Help Forum Motion

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 Feb 22nd 2018, 07:28 AM #1 Junior Member   Join Date: Feb 2018 Posts: 3 Motion The position of a particle is 6.8t^{3} i + 3 i ^ + 8t^{4} j m . What is the x component of the acceleration at time 3.2 s in unit of ms-2? (t denotes time in second.) My calculation: ( 6.8*3*3.2^{2} ) / 3.2 Why is it wrong? Thank you Last edited by hotk9911; Feb 22nd 2018 at 08:56 AM.
Feb 22nd 2018, 07:44 AM   #2
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Well acceleration is the second derivative of time with respect to distance for a start.

 3*3.2^{2}

Feb 22nd 2018, 07:53 AM   #3
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 Originally Posted by studiot Well acceleration is the second derivative of time with respect to distance for a start.
You just violated the forum rule regarding homework. See
Forum rule
 (m)No homework should be posted directly. Workings or any approaches to the questions should be shown to let others know you have made an effort or at least a try. It is to encourage people to learn but not to copy homework.
 The Helpers and the staff of the forum have agreed that they won't give a full answer to a problem posted with no attempt (except maybe in some cases). The Helpers are here to help you to understand your weaknesses by going through the asked questions with you and not here to solve your physics problems. It is imperative to show an attempt to a problem. If you don't know how to start, say it. Helpers will give you a push in the right direction.
I've mentioned this many times but its always been ignored.

Learning physics by doing homework fails when there's no struggle to solve difficult problems. Helping people in such cases is very useful unless the solution is simply given to them. You might think you're helping them by stating the aswer but you're actually hurting them.

 Feb 22nd 2018, 07:56 AM #4 Junior Member   Join Date: Feb 2018 Posts: 3 I got it. It should be (6.8*3*2*3.2) / 3.2=40.8. Thank you!
Feb 22nd 2018, 08:06 AM   #5

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 Originally Posted by Pmb You just violated the forum rule regarding homework. See Forum rule Must read before posting a problem : please show your attempt! I've mentioned this many times but its always been ignored. Learning physics by doing homework fails when there's no struggle to solve difficult problems. Helping people in such cases is very useful unless the solution is simply given to them. You might think you're helping them by stating the aswer but you're actually hurting them.
studiot's response is fine by me as he doesn't show how he did it. Call it more of a tease.

Otherwise, yes.
@hotk9911 : What have you been able to do?

-Dan
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 Feb 22nd 2018, 08:35 AM #6 Junior Member   Join Date: Feb 2018 Posts: 3 I know the acceleration should be the second derivative but I just miscalculate in my first calculation. Thanks again for reminding my careless mistake!
 Feb 22nd 2018, 09:10 AM #7 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 1,035 Well I'm comfortable with my assessment of most beginnings and offer advice accordingly. hotk9911 I thought you made one of those silly slips we all do. And you need congratulations for actually showing your attempt without being asked. Hopefully you will get some great advice here in future Last edited by topsquark; Feb 22nd 2018 at 10:26 PM.

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