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Potato Head October 5th 2009 12:14 AM

My oh my... Help me with Physics!
My brain feels like it's going to explode!
I'm only going to post one problem and hope to god that any help with that can help me with the other 5 or 6.
I don't understand a thing...

Do not just give me an answer, I need explanations and any equations you use.
From what I can tell I can't use F=MA unless I'm missing something.

4. Scientists are experimenting with a kind of gun that may eventually be used to fire payloads directly into orbit. In one test, this gun accelerates a 5.0-kg projectile from rest to a speed of 4.0 x 10^3 m/s. The net force accelerating the projectile is 4.9 x 10^5 N. How much time is required for the projectile to come up to speed?

Any help is appreciated.

Pelios October 5th 2009 01:13 AM

Re: My oh my... Help me with Physics!
You can use F=MA, using it you find the acceleration

A= F/M = 4.9 10^3/5.0 = 9.8 10^4m/s

and from V=AT we find time
T= V/A = 4.0 x 10^3/ 9.8 x 10^3 = 0.041s

I think that's how you do it.

tk338 October 5th 2009 01:26 AM

Re: My oh my... Help me with Physics!
Correct I believe... Haha bit slow on that one couldn't quite work out how the acceleration was so high.... then I saw it was a gun :p

Potato Head October 5th 2009 01:55 AM

Re: My oh my... Help me with Physics!
I have a quick question--
Is there any other way to get the time? My stupid book doesn't have that equation and it's only using F=ma.
I'm so confused, it makes sense what you did, and I understand. But my textbook is so complicated.

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