# Homework Help: Another gravity problem

1. Feb 25, 2005

### mohlam12

we have a shuttle in space taht is 518917 m above earth, if an astrinaut weight 900N, how much he will weight on the shuttle?

here is what i did so far,

the gravity on the shuttle = (6.67E-11* 6E24)/(518917+6.37E6)^2= 8.43m/ss

6.37E6 is the radius of earth in m
6.67E-11 is the universal gravitational system
6E24 is mass of earth in Kg

now his weight on earth is 900N --> 91.84 Kg

so in the shuttle he weights 91.84 / (9.8/8.43) = 79 Kg
i dont think that s right because if he weight 79Kg he is not gonna fly on the shuttle, and i think a gravity of 8.43 m/ss is too much for a shuttle that is 519 Km above earth ?!?!

2. Feb 25, 2005

### learningphysics

You've calculated the mass. You've calculated g on the shuttle. Weight is just mg=91.84*8.43=774N

3. Feb 25, 2005

### BobG

Everything is correct except for one thing.

kg is a measure of mass. Your mass doesn't change regardless of where you are. Your final answer has to be in Newtons.

In other words, the original mass (about 91.77 kg) times the gravity on the shuttle.

4. Feb 25, 2005

### tony873004

I think your weight would be 0. You'd only have weight if the shuttle could hover without orbiting at that altitude. Then you could compute the weight (w=ma) a = GM/(earth radius + altitude)^2 . But if the shuttle is orbiting, and you're in it, you're both in freefall and you are weightless. Verify this by stepping on a scale.

5. Feb 25, 2005

### mohlam12

but dont u think that for a shuttle that is 514 km above earth should have a gravity less than 8.43 m/s/s ?

6. Feb 25, 2005

### dextercioby

No,why...?Your calculations seem correct.And yes,the weight is 0,due to free fall...

Daniel.

7. Feb 25, 2005

### BobG

True, since he's not applying a force against anything (both he and the shuttle are 'falling' at the same rate).

But, unless it's a trick question, the 774 N is what I think the question wants.

8. Feb 25, 2005

### learningphysics

I don't think the question is asking that. It doesn't give the shuttle as being in orbit. I think it's simply asking the force exerted by the Earth on the astronaut.

9. Feb 25, 2005

### dextercioby

Then it must be a heck of a poor wording from the author...Any normal person would interpret "shuttle in space that is 518917 m above earth" as a shuttle in free fall."how much he will weight on the shuttle ??"...

Daniel.

10. Feb 25, 2005

### mohlam12

the shuttle is in orbit yeah :| so?

Last edited: Feb 25, 2005
11. Feb 25, 2005

### dextercioby

So,according to common sense and Newtonian physics,the weight is ZERO...

Daniel.