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April 18, 2014

Homework Help: Physics

Posted by sarah on Friday, February 9, 2007 at 10:12pm.

A 6100 kg rocket is set for vertical firing from the ground. If the exhaust speed is 1200 m/s how much gas must be ejected each second if the thrust a) is to equal the magnitude of the gravitaiotnal force on the rocker and b) is to give the rocket an inital upward acceleration of 21 m/s^2?

I do know that thrust is the rate at which the exhust is expelled times the velocity of exhust... I am not even sure if this is relevent to this problem. Pleasee guide me into the right direction.

Also can you explain how I would set up this problem? I really appeciate the time you guys put inot answering these questions. Thanks in advance for your help.

Forcenet= mass*acceleration

but momentum down= massgas*velocitygas
momentum/time= massgas/time *velocity
forcegas= massgas/time*velocity

and force net= force gas- weightrocket
force net= massgas/time*velocitygas - massrocket*g


Finally,
massgas/time*velocitygas - massrocket*g= mass*acceleration
In the first case, acceleration is zero.

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