Is answer in BMW book for problem 4.3 wrong?
Proof that book problem answer is wrong:
Since r0 and v0 are perpendicular, then satellite
must be at aporigee or perigee.
But ro
= I + J, hence
|ro| = sqrt(2)
and vo
= 2K hence |vo| = 2
v^2 u
Energy = ------ - ----
2
r
Hence Energy (calculated at perigee) = 4/2 –
1/sqrt(2) = 1.2928932
Since E>0, this is a hyperbola. Then must be a
perigee.
u
Energy = - ----- ---(1)
2a
To find ‘a’, Plug Energy in (1), and noting that
u=1, we get
1
1.2928932 = - -----
2a
hence a
= -0.3867295 DU
| I J K |
h = r0 x v0 = |
1 1
0 | = I (2) – J (2)
| 0 0 2 |
hence h = sqrt(4+4) = sqrt(8)
h^2
Now, p = ----
= h^2
u
Hence p = 8
p
To find e, from
rp = ---------------
1 + e cos(0)
(I can also use
p=a(1-e^2) to find e).
since rp = r0 = sqrt(2), then 1+e=8/sqrt(2)
e = 8/sqrt(2) –
1 =
4.656854
Now we can find r when satellite traveled 60 degree.
p 8
r = ---------------
= ---------------------- =
2.4035377 DU
1 + e
cos(60) 1 + 4.656854 cos(60)
Now I find v when satellite traveled 60 degrees
From
v^2 1
--- - ---
= Energy
2
r
But we found Energy and r from above, and since
Energy is constant, so solve for new v
v^2 = 2 (1.2928932 + 1/2.4035377)
v^2 = 3.417893173
v = 1.84875449
DU/TU
Now, the book gives this answer as to the velocity:
v = -0.348 I – 0.348 J + 1.5 K
then v = 1.57867286
DU/TU
as you can see, this answer does not agree with my
calculation.
I do not see where I am going wrong. Is the book
wrong or right?