Question

A 600 kg rocket is set for a vertical firing. If the exhaust speed is 1000m/s, the mass of the gas ejected per second to supply the thrust needed to overcome the weight of rocket is

• A. $117.6kg{s}^{-1}$
  
• B. $58.6kg{s}^{-1}$
  
• C. $6kg{s}^{-1}$
  
• D. $76.4kg{s}^{-1}$

Answer 1

The correct option is C $6kg{s}^{-1}$


Thrust =$u\frac{dm}{dt}=Mg$
or $\frac{dm}{dt}=\frac{Mg}{u}$
$=\frac{600\times 9.8}{1000}=6kg{s}^{-1}$