Calculating Initial Acceleration

[kencamarador]

calculate the initial acceleration of a 13 140 kg V-2 rocket bomb fired vertically, if the thrust of its engines is 2.63 x 10 to the power of 5 N. then calculate the rockets acceleration near "burn-out", when its mass is only 4170 kg.


So i did. Part 1.

Fnet = ma
a = fnet/m
20.01m/s^2= 263000/13140

but the correct answer is 10.2

 

[rude man]

You forgot to include gravitational force.

 

[kencamarador]

ah, right right.
Fg = 13140+9.8
=128772 N (Down)

Fnet= 263000-128772
= 134228 N (Up)

Acceleration= f/m
=10.2m/s^2 (Up)

Thx.