(a) The force diagram of the rocket will consist of the weight (W), and upward thrust force (F).
(b) The time taken for the rocket to reach the speed of 900 m/s is 36.7 s.
How to draw the force diagram for the rocket?
(a) The force diagram of the rocket will consist of the weight of the rocket acting downwards, and upward thrust force of the rocket
(b) The acceleration of the rocket is calculated by applying Newton's second law of motion as follows;
F(net) = ma
a = F(net) / m
The mass of the rocket is calculated from its weight formula;
w = mg
m = w / g
m = ( 40,000 ) / (9.8)
m = 4,081.63 kg
a = F(net) / m
a = (140,000 N - 40,000 N ) / 4,081.63
a = 24.5 m/s²
The time taken for the rocket to reach the speed of 900 m/s is;
t = v/a
t = (900 m/s ) / (24.5 m/s²)
t = 36.7 s