# Net force on astronaut (1 Viewer)

#### Karldahemster

##### Student
A rocket of mass 2000 tonnes, produces a constant thrust of 8x10^7N during liftoff by expelling 1500kg of exhaust gas per second.

Calculate the net force acting on an 85kg astronaut 30s after liftoff.

#### jazz519

##### Moderator
Moderator
a=T-mg/m

so T is constant = 8x10^7
m=(Initial mass of the rocket + fuel system) - (mass of fuel ejected)
= 2000x1000-1500x30
= 1955000 kg

so a=T-mg/m
= 8x10^7-1955000(9.8)/1955000
= 39.9207161125 m/s^2

F=ma
= 1955000(39.9207161125)
= 3393.26086957 N

• BLIT2014 and Squar3root

#### Karldahemster

##### Student
a=T-mg/m

so T is constant = 8x10^7
m=(Initial mass of the rocket + fuel system) - (mass of fuel ejected)
= 2000x1000-1500x30
= 1955000 kg

so a=T-mg/m
= 8x10^7-1955000(9.8)/1955000
= 39.9207161125 m/s^2

F=ma
= 1955000(39.9207161125)
= 3393.26086957 N
Thanks, that's what I thought however, the solution just used a=F/m so must have been incorrect.

#### jazz519

##### Moderator
Moderator
f=ma sorry on the last bit should be 85 instead of 1955000 (used it for the end answer but forgot to change it in the typed one)