Speed of a Rocket far from Earth

  • #1

Homework Statement



A rocket is launched straight up from the earth's surface at a speed of 1.60×10^4 m/s.
What is its speed when it is very far away from the earth?

Homework Equations


F= (GMm)/r^2
G= 6.67 X 10^-11
M= 5.98 X 10^24

Potential Energy = (Gm1m2)/r
Kinetic Energy = 1/2mv^2
Escape velocity= 11200 m/s

The Attempt at a Solution



My first attempt was to take the speed of the rocket (1.60 X 10^4) and subtract it from the escape velocity. This gave me 4800 m/s. This assignment is online and the program said that answer is incorrect. Now I am not sure how to approach the problem. Does anyone have advice as to how to start this problem? All help is greatly appreciated. Thank you.
 

Answers and Replies

  • #2
D H
Staff Emeritus
Science Advisor
Insights Author
15,393
685
Try using conservation of energy.
 
  • #3
Conservation of energy was my second attempt. I set it up as this:

P.E. + K.E. = K.E. + P.E.


OH!!!!!!!!!!!! I see. Dang, for some odd reason the first time I tried this approach I used 9.8 as the value for P.E. ...how foolish. I see now. Thank you so much. Man, I cannot afford to do that on a test. Thanks again.
 

Related Threads on Speed of a Rocket far from Earth

  • Last Post
Replies
4
Views
575
Replies
2
Views
3K
Replies
3
Views
1K
Replies
5
Views
3K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
11
Views
587
Replies
2
Views
1K
  • Last Post
Replies
7
Views
5K
Top