Force Needed to Hold Rocket Down

[joel amos]

Q: The motors of a 1,000 kg rocket standing vertically on the ground are being tested. Fuel is being burned at the rate of 5.0 kg/s with an exhaust speed of 2.8 km/s. Find the force needed to hold the rocket down.

Attempt: I'm not really sure how to go about this question. I've thought about it a lot, but don't understand how to solve it. I think the force needed to hold it down would be equal to the natural force plus mg (9.8 kN), but I'm not sure how to find the natural force with the given information of the combustion rate and exhaust speed.

Thanks for helping!

 

[lewando]

Thrust = (dm/dt)V, where dm/dt is the mass flow rate and V is the exhaust speed.