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?