Help on Physics homework

1. Mar 18, 2008

iamwilson

A rocket is fired in deep space, where gravity is negligible
If the rocket has an initial mass of 6000kg and ejects gas at a relative velocity of magnitude 2000m/s , how much gas must it eject in the first second to have an initial acceleration of 25.0m/s^2 ?

im stuck on this problem, can anyone help me on it thanks!

2. Mar 18, 2008

Mathemaniac

3. Mar 18, 2008

Snazzy

You can figure out the total force using F=ma

Then you can use the impulse-momentum theorem to calculate the amount of fuel needed to be ejected in the first second.

4. Mar 18, 2008

kamerling

the mass loss of the rocket is big enough to be significant, given the fact that the
acceleration was given with 3 significant digits.
Given this, it think "how much gas must it eject in the first second to have an initial acceleration of 25.0m/s^2" is ambiguous.
I think "how much gas must it eject in the first second to have a constant acceleration of
25.0m/s^2 during this time" is the most reasonable interpretation.
You will need the rocket equation v = v_ex ln(m_0/m) that you gave in your other post for this. you know v, v_ex and m_0 (initial mass of the spaceship).

5. Mar 18, 2008

iamwilson

sorry, this is my first time using this website, so i don't know all the rules, but it's is extremely helpful