The rocket launch and changing gravity

1. Mar 6, 2012

marco12345a

When a rocket is launched, it starts not with velocity zero, but with the rotation velocity which the Earth gives it. Thus if a rocket is launched eastward, it requires a smaller boost (and if westward, a larger one) to achieve orbit. with a latitude of 31.1 degrees, cos(31degrees) 24902/24 = 393.11 ms/s

To escape velocity on earth = (2G Mearth / r earth) = 11200ms-1
So the total velocity that needed for the rocket = 11200 - 393.11= 10806.99ms-1

I am trying to find the total energy that is needed for the rocket of 1000kg to escape velocity

i used the question
m = 1000 x 9.8 N

E= 1/2 m^2
= 5.84 X 10^10 J

my question is : as the further you are away from earth, there will be less gravity. So if i use that equation, would that be accurate assume there is no air friction and the mass of the rocket doesnt change due to the loss of fuel

2. Mar 6, 2012

PhysicoRaj

That would be close enough! But the problem is that the accuracy falls as u go on neglecting decreasing mass due to consumption of fuel.

3. Mar 6, 2012

marco12345a

should i use the equation of E= 1/2 m^2 ?

4. Mar 6, 2012

PhysicoRaj

If u r calculating energy, then of course it'll do. note that, E=1/2mv^2=GMm/r

5. Mar 6, 2012

marco12345a

but doesnt the changing gravity affect the m ?

6. Mar 6, 2012

PhysicoRaj

Yes but if u really want to solve it u will hav to take an average of that.

7. Mar 6, 2012

PhysicoRaj

more than that...changing mass is a prob.

8. Mar 6, 2012

marco12345a

for example if a rocket is 1000 kg on earth , what would the gravity be when it is at 300m

9. Mar 6, 2012

PhysicoRaj

If u r dealing with mass, it would be 1000Kg itself. if u r dealing about wight, itll bcom
W=mg
=1000*g
g= gravitational acceleration at 300mts
u manipulate it...
g=w/m
=w/1000
ul hav to know its weight there.

10. Mar 6, 2012

marco12345a

how do you find the changing gravity ?

11. Mar 6, 2012

PhysicoRaj

12. Mar 6, 2012

PhysicoRaj

the gravity dosnt change preferentially at 300mts
observ: g=9.806 in 0mts
g=9.803at 1000mts

ok bye..

13. Mar 6, 2012

marco12345a

okay thank you very much