a question (1 Viewer)

[GaganDeep]

A rocket has a mass of 2x10^6 kg of which 80% is fuel. It develops a thrust of 6.0 x10^7 N. Its rocket burn at a rate of 2x10^5 kg min^-1

Calculate the acceleration of the rocket at time 4 minutes.

Umm i am kind of confused on thi.s

 

[rama_v]

A rocket has a mass of 2x10^6 kg of which 80% is fuel. It develops a thrust of 6.0 x10^7 N. Its rocket burn at a rate of 2x10^5 kg min^-1

Calculate the acceleration of the rocket at time 4 minutes.

Umm i am kind of confused on thi.s

The principle to remember here is that as the rocket is burning fuel, it is losing mass (i.e., the fuel it is carrying is being burnt, reducing the overall mass of the rocket). Since the force of the engines is constant, according to the formula F = ma, the acceleration must increase if the mass decreases and F is constant.

So, Mass of fuel = 1.60 x 10⁶ kg
Mass of fuel used up in 4 minutes = 4 x 2 x 10⁵ kg = 8 x 10⁵kg

Therefore, Mass of Rocket after 4 minutes = Mass of Rocket initially - Mass of Fuel used up

= 2 x 10⁶ - 8 x 10⁵ = 1.20 x 10⁶ kg

F = ma, so a = F/m = 6 x 10⁷/1.20 x 10⁶ = 50 ms^-2

 

[GaganDeep]

the answers is 40 ms^-2.
also i thought u would need to use (t-mg)/m
but what is m

(6x10^7 -9.8 X m)/m
how do u claculate m?