1. Nov 8, 2007

### get_rekd

When the space shuttle is flying in space, away from the influence of any gravitational fields, its engines provide a total thrust of 2.4 X 10^7 N. If the shuttle weighs 2.0 X 10^7 N on the surface of the earth, what is its acceleration? (use g=10 m/s^2)

Fg= (2.0 X 10^7 N)(10 m/s^2)
= 2.0 X 10^8 N m/s^2

Fnet= (2.0 X 10^8 N m/s^2)-(2.4 X 10^7 N)
= 1.76 X 10^8 N m/s^2

a= 1.76 X 10^8

I have absolutely no clue how to do this but this is what I have figured out can someone please explain for me?

2. Nov 8, 2007

### tyco05

If the shuttle WEIGHS 2 x 10^7 N on earth, then this is the force.

What you need to calculate is the mass of the shuttle using F = mg

The question states that it is away from the influence of any gravitational fields, so the net force is given by the thrust.

Using F = ma you can then determine the acceleration.

3. Nov 8, 2007

### get_rekd

I'm sorry but I still don't understand.

so the mass of the shuttle would be 2 x 10^8 N then?
and Fnet= 2.4 X10^7?

4. Nov 8, 2007

### aq1q

hey, lol this looks awefully similar to a problem i have in my textbook.. but anyway
its like how he said, u have to remember that mass doesn't change, weight does. So in earth, you are given a weight. Therefore, you can find the mass of the shuttle. you see

W=mg (use 10 for your g), then once you have that..use F(thrust)= ma

simple heh

5. Nov 8, 2007

### aq1q

mass of the shuttle is in KG, and force is in NEWTONS (N), it is important to get the units right..

6. Nov 8, 2007

### tyco05

OK.... If something weighs 2 x 10^7 N, then this is the force with which gravity is pulling it towards Earth.

Its mass can be determined from a rearrangement of F= mg (mass is measured in kg)

Now, if we have a mass shooting through space, being pushed by an engine with a force of 2.4 x 10^7 N, we can figure out its acceleration using a rearrangement of F = ma.

Note that these are two different cases, so the F in each is different.

7. Nov 8, 2007

### aq1q

right, use W=mg, because well its not wrong technically, but weight is a force, and in physics you generally use W for weight instead of Fg. anyway tell me what u get

8. Nov 8, 2007

### aq1q

and remember the mass doesn't change

9. Nov 8, 2007

### get_rekd

I think my head is all goofed up today I just cant seem to do math correctly haa..

So I would then take,
2.4 X 10^7 N = (2.0 X 10^8 N)(a)
-2.0 X 10^8 N -2.0 X 10^8 N
-1.76 X 10^8 N = a

??

10. Nov 8, 2007

### aq1q

lol, atleast you realized that is wrong.. but look acceleration is (m/s^2) force is (kg m/s^2) aka: mass x acceleration. anyway lol
2.0x10^7 N= mg (10=g)
then take that mass
2.4x10^7N=ma (a is what you solving for) if i do anything more, i will end up solving the problem

11. Nov 8, 2007

### tyco05

Not quite.

Your 2.0 x 10^8 is wrong.

W = mg

2.0 x 10^7 = m (10)

m=?

then use F(thrust) = ma

12. Nov 8, 2007

### get_rekd

okay so then...
2.0 X 10^7 = m(10)
-10 -10
1.9 X 10^7 = m

2.4 X 10^7 N = 1.9 X 10^7(a)
-1.9X10^7N -1.9X10^7N

5.0 X 10^6 N = a

13. Nov 8, 2007

### tyco05

You are subtracting where you need to divide. - do the calculations again.

Other than that it looks ok.

Also, remember your units! acceleration is measured in m/s^2

14. Nov 8, 2007

### aq1q

LOL!! sorry, not to be mean, but that was funny

15. Nov 8, 2007

### get_rekd

alright so. For the 8th try haha! 2.4 X 10^7 N = 1.9 X 10^7 N a
then I divide 2.4 X 10^7 N by 1.9 X 10 ^7 N and get a
so a = 1.3 m/s^2

16. Nov 8, 2007

### aq1q

nope.. i dont know what to say lol,

17. Nov 8, 2007

### aq1q

okay so then...
2.0 X 10^7 = m(10)
-10 -10 (ERROR)-- fix that
1.9 X 10^7 = m (fix that)

2.4 X 10^7 N = 1.9 X 10^7 (fix that) (a)
-1.9X10^7N -1.9X10^7N (DIVIDE not multiply) 6=2x3 --> 3=6/2 or 2=6/3 (6-3 doesn't = 2-3)

5.0 X 10^6 N = a

18. Nov 8, 2007

### get_rekd

Thanks a lot for the help guys. I appreciate it!

19. Nov 8, 2007

### get_rekd

alright I think I figured it out now I hope to the lord.

2.0 X 10^7 N = m(10)
------------ -------
10 10

m= 2.0 X 10^6 N

2.4 X 10^7N = 2.0 X 10^6 N a
------------- ---------------
2.0X10^6N 2.0X10^6N

a= 12 m/s^2

20. Nov 8, 2007

good lol :)