# Rocket Thrust Force

1. Nov 12, 2007

### Sucks@Physics

A toy rocket, of mass 90g, acheives a velocity of 80m/s after 3.0s when fired straight up. What average thrust force does the rocket engine exert?

I dont' know what formula to use for this

2. Nov 12, 2007

### hage567

Can you find the average acceleration?

3. Nov 12, 2007

### aq1q

is this held in earth where gravity exists? lol, i know its a dumb question, but sometimes during my life, i have done problems like these without the involvement of gravity.

Last edited: Nov 12, 2007
4. Nov 13, 2007

### Sucks@Physics

avg acceleration = 26.667m/s and lol yea its on earth

5. Nov 13, 2007

### Sucks@Physics

no help?

6. Nov 13, 2007

### hage567

Acceleration is in m/s^2.

So what's Newton's second law?

7. Nov 13, 2007

### Sucks@Physics

what i did is...

Fnet = (m*v)/t

Fnet = (.09*80)/3 = 2.4N

What did i do wrong?

8. Nov 13, 2007

### Sucks@Physics

Am i not supposed to be solving for Fnet?

9. Nov 13, 2007

### Sucks@Physics

Can some1 help i ahve to have this finished by tomorrow and i'm doing it wrong

10. Nov 13, 2007

### Feldoh

Does it give you a rate at which the mass of the rocket is changing?

11. Nov 13, 2007

### Sucks@Physics

I think i'm neglecting that.

12. Nov 13, 2007

### aq1q

ok, start out by drawing a free-body diagram. since the thrust is accelerating upwards.. thrust must me greater than weight. therefore Ft-W=Ma soo Ft=w+ma, right?

Solve for a, and then just plug and chug..

13. Nov 14, 2007

### Sucks@Physics

sweet thanks, i get it now

14. Nov 18, 2011

### physicnoob101

hey, i have the same question, but what does w stand for? since m = mass, Ft = force of thrust anf a = acceleration (right)? then what is w?

15. Nov 18, 2011

### SteamKing

Staff Emeritus
What force must the rocket thrust counteract in order for the rocket to rise?