Comments on: Equations of Motion

By: Brandon

Brandon — Wed, 18 Mar 2009 00:57:18 +0000

Thanks Dave, I think you’ve solved by D=d/dt operator, isn’t it?

By: trevorpythag

trevorpythag — Sun, 08 Mar 2009 17:01:20 +0000

we can let m2= -100
so that m = 10i
then
s=e0(Ecos10t + iFsin10t)
so s = (Ecos10t + iFsin10t)
and subsubsiting in the conditions given we can find the values of E and F

By: Nina

Nina — Fri, 06 Mar 2009 18:05:38 +0000

Me too Brandon, I need it for preparing mechanics exam

By: Brandon

Brandon — Wed, 04 Mar 2009 04:08:21 +0000

Dave, I always follow your discussion with miss Denaya. I think this is very educational discussion. Really, until now I try to solve challenge from miss Denaya to solve s”(t)+100s(t)=0 by integration, but sorry I’ve no idea to do it. Can you or all visitors here help me…

By: trevorpythag

trevorpythag — Sun, 01 Mar 2009 12:17:21 +0000

sorry that was a typo,
c=atan(v0/10s0)

well done in spotting it

By: Jeff

Jeff — Sun, 01 Mar 2009 00:30:35 +0000

Sorry dave, whether you miss in writing
c=atan(v0.10s0). I see on Denaya’s solution the initial phase in form c=atan(v0/10s0), or which one the right answer?thx.

By: Denaya Lesa

Denaya Lesa — Wed, 25 Feb 2009 13:53:15 +0000

@trevorpythag,

Thanks for your help in proving my solution posted previously. From your proof above, Denaya can take a conclusion that the pythagoras relation and all of your trigonometric relation posted previously are very required in solving physics’s problems, isn’t it.
Good Luck..@trevorpythag.

See you later,
Denaya Lesa.

By: trevorpythag

trevorpythag — Tue, 24 Feb 2009 19:50:05 +0000

We can prvoe your solutions for s(t) and v(t) from my soltuion if we let s(t) = rsin(10t + c) where we can work out c and r by using the identity for compound sin (see my post on this) so
s(t) = rsin10tcosc + rcos10tsinc
and by comparing co-efficents
rcosc = v0/10 and rsinc = s0
so c = atan(v0/10s0) as you showed.
we can then find r by squaring the 2 equations to get

This can also be done in a similar way for v(t)
r^2 (cosc^2 + sinc^2) = (v0/10)^2+s0^2

so we know can write s(t) as
s(t)=√[s0^2+(v0/10)^2]*cos(10t-atan(v0/10s0))
as you showed using the SHM equations.

By: Denaya Lesa

Denaya Lesa — Mon, 16 Feb 2009 05:32:03 +0000

Thank @Nicola for your nice comment. Important to be known that all of post’s Rohedi’s Family at so many math blogs would be dedicated for our nation Republic of Indonesia. Thank’s for @trevorpythag at al who accept Denaya’s comments at this math blog as well.

Again, thank you @Nicola,
my best regards,

Denaya Lesa.

By: Nicola

Nicola — Sun, 15 Feb 2009 12:20:59 +0000

Hello,

I think that you explanation is excellent :) you obviously put a lot of effort into it.

Well done