Rocket thrust, mass, speed given initial m and fuel consumption rate?

1. Mar 12, 2013

rockchalk1312

A rocket, which is in deep space and initially at rest relative to an inertial reference frame, has a mass of 59.5E5 kg, of which 7.39E5 kg is fuel. The rocket engine is then fired for 300 s, during which fuel is consumed at the rate of 480 kg/s. The speed of the exhaust products relative to the rocket is 3.55 km/s.
(a) What is the rocket's thrust? After the 300 s firing, what are (b) the mass and (c) the speed of the rocket?

F=ma

Found mass by doing (300s)(480kg/s)=144000kg
Subtracted from 59.5E5-144000=5.81E6 kg

But I have no idea where to start on a and c. Thank you!

2. Mar 12, 2013

CWatters

A hint for question a). Think about the units in Newtons equation..

Force = mass * acceleration

The units are..

= Kg * m/s^2

rearrange that a bit.

3. Mar 12, 2013

rude man

I would use the momentum integral: ∫Fdt = Δp.

4. Mar 13, 2013

sankalpmittal

And I would use a direct formula for calculating thrust in a variable mass system: Mass rejection.... :tongue:

5. Mar 13, 2013

rude man

Chaqu'un a son gout ...