<p>As a hint: a force directed inward does not change the angular momentum, and therefore does not change the semi-major axis nor the period. It's not clear which angle you're talking about, but knowing that the semi-major axis did not change should let you set the problem up as a simple geometry problem.</p>

CC BY-SA 3.0
2015-01-04T00:13:37.527Z
But the force did change the angular momentum, otherwise it would stay in the circular orbit. In fact, it increased the momentum by increasing the velocity. There are now two force towards the earth, the applied force and gravity.
LDC3
CC BY-SA 3.0
2015-01-04T00:27:01.867Z
Nope. It changed the momentum, but not the angular momentum. That was the gist of Kepler's second law, that an orbit sweeps out equal areas in equal time. He didn't know about angular momentum (or about momentum), and didn't know that for it to be constant meant that the force was a central force, directed toward the Sun. (He didn't know about forces, either.) Your thrust is defined as a "sudden" thrust, meaning it's momentary, and the only force still acting on the satellite is gravity.
ganbustein
CC BY-SA 3.0
2015-01-04T00:44:33.623Z
Unfortunately, I can't include an image. If the satellite has a velocity vector of (12m/s,0) before and (12m/s,5m/s) after, how is that not a change in angular momentum. After all, the satellite is in the same position and the magnitude of the velocity changed from 12m/s to 13m/s and it's in a different direction.
LDC3
CC BY-SA 3.0
2015-01-04T00:48:53.280Z
I don't want to see your image. You need to learn the difference between `angular momentum` and `(linear) momentum`.
ganbustein
CC BY-SA 3.0
2015-01-04T01:14:19.397Z
Telling me that they are different doesn't help. Why does the angular momentum not change?
LDC3
CC BY-SA 3.0
2015-01-04T01:39:56.370Z
Think it through.
ganbustein
CC BY-SA 3.0
2015-01-03T23:49:39.097Z
2015-01-03T23:49:39.097Z
ganbustein
<blockquote>
<p>A satellite which is moving around a planet of mass <span class="math-container">$M$</span> in a circular orbit of radius <span class="math-container">$R$</span> is given a sudden thrust into the center of the planet, so that it deviates an angle <span class="math-container">$a$</span>.</p>
<p>Find the latus-rectum <span class="math-container">$l$</span> and the eccentricity <span class="math-container">$e$</span> of the new orbit.</p>
</blockquote>

CC BY-SA 3.0
2015-01-03T04:19:17.173Z
What do you mean by "into the center of the earth"? Do you mean towards the center of the earth?
LDC3
CC BY-SA 3.0
2015-01-03T10:28:39.133Z
i mean **directing** to the centre of the planet.
NIkhil Reddy Ramolla
CC BY-SA 3.0
2015-01-03T12:17:01.587Z
This question appears to be off-topic because it is about homework.
David Hammen
CC BY-SA 3.0
2015-01-03T14:13:05.253Z
@DavidHammen AFAIK homework [isn't itself off topic](http://meta.astronomy.stackexchange.com/questions/87/homework-policy/88#88) in Astronomy. That said, the question could probably use some rewording.
Mitch Goshorn
CC BY-SA 3.0
2015-01-03T16:13:44.727Z
Don't expect to get your homework done by others. Put some effort into it, show what you tried. Say where you stumble.
guntbert
<orbit><gravity>
Question: calculating orbit using another orbit
NIkhil Reddy Ramolla
# Question: calculating orbit using another orbit

(Asked by: username_0 on 2015-01-03)

> A satellite which is moving around a planet of mass $M$ in a circular orbit of radius $R$ is given a sudden thrust into the center of the planet, so that it deviates an angle $a$.
>
> Find the latus-rectum $l$ and the eccentricity $e$ of the new orbit.

**Tags:** orbit, gravity
> **Comments:**
> **username_1**: What do you mean by "into the center of the earth"? Do you mean towards the center of the earth?  
> **username_0**: i mean **directing** to the centre of the planet.  
> **username_2**: This question appears to be off-topic because it is about homework.  
> **username_3**: @DavidHammen AFAIK homework [isn't itself off topic](http://meta.astronomy.stackexchange.com/questions/87/homework-policy/88#88) in Astronomy. That said, the question could probably use some rewording.  
> **username_4**: Don't expect to get your homework done by others. Put some effort into it, show what you tried. Say where you stumble.  

---

## 1 answers

### Answer by username_5 on 2015-01-03. Score: 1

As a hint: a force directed inward does not change the angular momentum, and therefore does not change the semi-major axis nor the period. It's not clear which angle you're talking about, but knowing that the semi-major axis did not change should let you set the problem up as a simple geometry problem.

> **Comments:**
> **username_1**: But the force did change the angular momentum, otherwise it would stay in the circular orbit. In fact, it increased the momentum by increasing the velocity. There are now two force towards the earth, the applied force and gravity.  
> **username_5**: Nope. It changed the momentum, but not the angular momentum. That was the gist of Kepler's second law, that an orbit sweeps out equal areas in equal time. He didn't know about angular momentum (or about momentum), and didn't know that for it to be constant meant that the force was a central force, directed toward the Sun. (He didn't know about forces, either.) Your thrust is defined as a "sudden" thrust, meaning it's momentary, and the only force still acting on the satellite is gravity.  
> **username_1**: Unfortunately, I can't include an image. If the satellite has a velocity vector of (12m/s,0) before and (12m/s,5m/s) after, how is that not a change in angular momentum. After all, the satellite is in the same position and the magnitude of the velocity changed from 12m/s to 13m/s and it's in a different direction.  
> **username_5**: I don't want to see your image. You need to learn the difference between `angular momentum` and `(linear) momentum`.  
> **username_1**: Telling me that they are different doesn't help. Why does the angular momentum not change?  
> **username_5**: Think it through.  

---

