help with 'simple' question (1 Viewer)

[me dumb]

gah i dnt get this
A rocket has a mass of 30000kg, including 25000kg of fuel. It develops a 360000N thrust. calculate:
a)its acceleration at lift-off
b)the theoretical maximum acceleration of the rocket
c)the g-force by an astronaught under maximum conditions

i just wanna see what everone else gets before i ask the part im confused about
thanks

 

[Bernie Mac]

ok i sorta used this equation

a=f/m=T-(mg)/m
so you just use T-(mg)/m where T is equql to the thrust or force
but i did something weird and doesn't look like what it should be anyways

360000-(30000x9.8)/30000
=2.2ms to minus 2(acceleration)

so that should be initial for (a) but for maximum accel. i think its when fuel completely burns out so 30000-25000 =5000
therefore 5000-(5000x9.80/5000
=8.8 ms acceleration

therefore g force is apparent weight on true weight therefore
g+a/9.8
therefore 9.8=8.8/9.8
= about 2 g

but i think somethings wrong cos it seems so small

 

[me dumb]

ok i sorta used this equation



so that should be initial for (a) but for maximum accel. i think its when fuel completely burns out so 30000-25000 =5000
therefore 5000-(5000x9.80/5000
=8.8 ms acceleration

when was this in our syllabus lol?
in the bold part did u mean 360000
if u put that in then u get the right answer of 62.2ms^-2
the last part i knew how to do, this new answer will change the answer for c obviously.
thanxs for ur help its the correct way