• We have a few events lined up for the October school holidays!
    Watch this space...

Net force on astronaut (1 Viewer)

Karldahemster

Student
Joined
Dec 16, 2016
Messages
89
Gender
Male
HSC
2018
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

Well-Known Member
Joined
Feb 25, 2015
Messages
1,029
Location
Sydney
Gender
Male
HSC
2016
Uni Grad
2021
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
 

Karldahemster

Student
Joined
Dec 16, 2016
Messages
89
Gender
Male
HSC
2018
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

Well-Known Member
Joined
Feb 25, 2015
Messages
1,029
Location
Sydney
Gender
Male
HSC
2016
Uni Grad
2021
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)
 

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top