# Launching from Mars

1. Oct 25, 2008

### soupastupid

1. The problem statement, all variables and given/known data
The Radius of Mars is R_m
its mass is m

The radius of Mars (from the center to just above the atmosphere) is R_m and its mass is m. An object is launched from just above the atmosphere of mars.

A) what is the object's initial velocity if its final velocity is V_f

2. Relevant equations

a=(v^2)/R <--wat v is this?
W=deltaKE

3. The attempt at a solution

i dont know how to start

im thinking i need to calculate the gravity from mars?
but if all im given is mass and radius
how do i calculate it?

i need to find the amount of work done by mars right?

Last edited: Oct 25, 2008
2. Oct 25, 2008

### lax1113

I think you need to use Newtons universal gravity law....

F=(GM1M2)R^2

This means that the force is equal to the constant G (6.67X10^-11) multiped by both masses, all of this divided by the distance between them squared.

this will get you the Force.

So now you have force, you know that Fnet=ma, so the acceleration will be {(Gm1m2)/R^2}/m

finally, Vf^2-Vo^2=2a(x), so you simply solve using the above equation as a, and they just say to use Vo i believe
I dont think this is a problem you shoudl get numbers for, it seems like a concept that you just want to work through with different equations and not really use numbers.

This is just from what I understand.

Good luck!

3. Oct 26, 2008

### soupastupid

im solving for Vo

the object is launched from above the atmosphere

im given the distance between object and mars (R_m)
and I'm given the weight of mars (m)

and I'm given Vf of the object

so what I did (but I did not get a good answer)

was use

F=Gm1m2/r^2

m1 = object
m2 = mars
r=distance from mars and object

so the F equals

F= Gm1m2/(R_m)^2

and then I think I'm suppose this formua

total W = deltaKE

F*d = .5m1vf^2 - .5m1vo^2

but how do I find d?

I think this is right

how do I use

vf^2-vo^2 = 2a (x) <--whats x ?

4. Oct 26, 2008

### lax1113

With what you have you won't be able to find work and finding energy is also not going to work out. I can't help if you dont supply numbers, I solved it simply with the units, plugging the numbers in should have yielded the answer.

From what I can understand by your explanation that is anyway, it doesn't seem like work is in anyway involved.