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Subject: Help with Physics

Now go make me some tea.

Calculate the speed of a 8.0 x 10^4 kg object if the kinetic energy is 109J.

The answer says it's 1.7 x 10^2 m/s, but I didn't get it. Can someone help me?

The formula is KE=1/2*mv^2

  • 11.27.2012 9:21 AM PDT
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109=((8*10^4).5)v^2

square root of 109/((9*10^4).5)= velocity

  • 11.27.2012 9:23 AM PDT

Now go make me some tea.


Posted by: Heart of Stone
109=((8*10^4).5)v^2

square root of 109/((9*10^4).5)= velocity

Is 8 x 10^4 80000, or 800000?

  • 11.27.2012 9:24 AM PDT

Posted by: Alex Mac Kee
If pen­ises were planes Jimmy's mouth would be an airport


Posted by: DarkBen64
Don't punch a British kid, the queen'll come after you.

v = [sqrt] (2KE / m)

So

v = [sqrt] (218 / 80000)

[Edited on 11.27.2012 9:26 AM PST]

  • 11.27.2012 9:25 AM PDT


Posted by: Heart of Stone
109=((8*10^4).5)v^2

square root of 109/((9*10^4).5)= velocity


thats not the right answer even though the equation is set up right.

OT: did you write all the numbers down correctly? any other information given that you missed?

  • 11.27.2012 9:26 AM PDT

Now go make me some tea.


Posted by: MarkFanous

Posted by: Heart of Stone
109=((8*10^4).5)v^2

square root of 109/((9*10^4).5)= velocity


thats not the right answer even though the equation is set up right.

OT: did you write all the numbers down correctly? any other information given that you missed?

No, it comes straight from the book itself.

  • 11.27.2012 9:26 AM PDT
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Posted by: TheDerRitter

Posted by: Heart of Stone
109=((8*10^4).5)v^2

square root of 109/((9*10^4).5)= velocity

Is 8 x 10^4 80000, or 800000?

Are your units correct? It's 80000 by the way.

[Edited on 11.27.2012 9:30 AM PST]

  • 11.27.2012 9:28 AM PDT

Posted by: Alex Mac Kee
If pen­ises were planes Jimmy's mouth would be an airport


Posted by: DarkBen64
Don't punch a British kid, the queen'll come after you.

8 * 10^4 is 80000, four zeroes

Your numbers may be wrong

  • 11.27.2012 9:28 AM PDT

Now go make me some tea.


Posted by: Heart of Stone

Posted by: TheDerRitter

Posted by: Heart of Stone
109=((8*10^4).5)v^2

square root of 109/((9*10^4).5)= velocity

Is 8 x 10^4 80000, or 800000?

Are your units correct?

Everything is correct. I just don't understand how to get the answer.
The problem came from the book.


Posted by: teh Chaz
8 * 10^4 is 80000, four zeroes

Your numbers may be wrong

I did the problem with 80000, I was just making sure 800000 wasn't the solution.

[Edited on 11.27.2012 9:30 AM PST]

  • 11.27.2012 9:29 AM PDT

Posted by: Alex Mac Kee
If pen­ises were planes Jimmy's mouth would be an airport


Posted by: DarkBen64
Don't punch a British kid, the queen'll come after you.

If it has that mass and it's going at the speed it says the answer is then its KE would be 1.156 * 10^9

Something is off, check your values and units

  • 11.27.2012 9:31 AM PDT

i get the 1.7 part but not the right scientific notation. Are you sure that the mass is correct?

  • 11.27.2012 9:31 AM PDT
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OP, think of it in physical terms. A mass that large with an energy that small exerted on it shouldn't be able to go that fast.

  • 11.27.2012 9:31 AM PDT

Now go make me some tea.


Posted by: teh Chaz
If it has that mass and it's going at the speed it says the answer is then its KE would be 1.156 * 10^9

Something is off, check your values and units

I got that too. I honestly don't know what it is. I made sure EVERYTHING is correct.

Could 1.1 be from rounding?

  • 11.27.2012 9:32 AM PDT

GOAT

Sounds like the answer is written wrong.

  • 11.27.2012 9:33 AM PDT

Now go make me some tea.


Posted by: BlackHeaven
Sounds like the answer is written wrong.

That's what I'm thinking too.

I'm gonna go talk to my physics teacher real quick.

[Edited on 11.27.2012 9:34 AM PST]

  • 11.27.2012 9:33 AM PDT

nvm

[Edited on 11.27.2012 9:34 AM PST]

  • 11.27.2012 9:33 AM PDT

Delta. Alpha. November. Indigo. Echo. Lima.

Make sure the energy isn't given in Giga Joules or the mass in grams etc.

  • 11.27.2012 9:36 AM PDT
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OP, can you post a picture of the problem in the book? Because I'm coming out with .052 meters/sec.

  • 11.27.2012 9:36 AM PDT


Posted by: Heart of Stone
OP, think of it in physical terms. A mass that large with an energy that small exerted on it shouldn't be able to go that fast.
It's not necessarily a good idea to think like that. A mechanics paper once had a ship that travelled through a lighthouse.

  • 11.27.2012 9:41 AM PDT

Now go make me some tea.

Alright, I got the answer, but the answer in the book was in significant figures, so the answer was v=165m/s but the book said 1.7 x 10^2m/s.

My teacher said it's the same answer, and that the book worded it wrong.

  • 11.27.2012 9:41 AM PDT
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Posted by: DarkBen64

Posted by: Heart of Stone
OP, think of it in physical terms. A mass that large with an energy that small exerted on it shouldn't be able to go that fast.
It's not necessarily a good idea to think like that. A mechanics paper once had a ship that travelled through a lighthouse.

That's a little strange.

  • 11.27.2012 9:42 AM PDT


Posted by: Heart of Stone

Posted by: DarkBen64

Posted by: Heart of Stone
OP, think of it in physical terms. A mass that large with an energy that small exerted on it shouldn't be able to go that fast.
It's not necessarily a good idea to think like that. A mechanics paper once had a ship that travelled through a lighthouse.

That's a little strange.
Yeah, but it happens unfortunately.

  • 11.27.2012 9:43 AM PDT
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Posted by: TheDerRitter
Alright, I got the answer, but the answer in the book was in significant figures, so the answer was v=165m/s but the book said 1.7 x 10^2m/s.

My teacher said it's the same answer, and that the book worded it wrong.

Could you show your work?

  • 11.27.2012 9:43 AM PDT


Posted by: TheDerRitter
Alright, I got the answer, but the answer in the book was in significant figures, so the answer was v=165m/s but the book said 1.7 x 10^2m/s.

My teacher said it's the same answer, and that the book worded it wrong.


we know it meant 170 m/s, but the equation doesnt give you 170 m/s, it gives you .52 or whatever

  • 11.27.2012 9:44 AM PDT

Now go make me some tea.


Posted by: MarkFanous

Posted by: TheDerRitter
Alright, I got the answer, but the answer in the book was in significant figures, so the answer was v=165m/s but the book said 1.7 x 10^2m/s.

My teacher said it's the same answer, and that the book worded it wrong.


we know it meant 170 m/s, but the equation doesnt give you 170 m/s, it gives you .52 or whatever

What? how did you get that?

  • 11.27.2012 9:45 AM PDT

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