A Diwali rocket is ejected $0.05 \mathrm{kg}$of gases per second at a velocity of $400 \mathrm{m}/\mathrm{s}$. The accelerating force on the rocket is 

A Diwali rocket is ejected $0.05 \mathrm{kg}$of gases per second at a velocity of $400 \mathrm{m}/\mathrm{s}$. 

The accelerating force on the rocket is $20 \mathrm{N}$.
Given,
Mass $\mathrm{m}=\mathrm{ }0.05 \mathrm{kg}$
Velocity $\mathrm{v} =\mathrm{ }400 \mathrm{m}/\mathrm{s}$
Time $\mathrm{t} =\mathrm{ }1 \sec$
Using the formula  $\mathrm{v}=\mathrm{u}+\mathrm{at}$, since the initial velocity of the rocket is zero, then $\mathrm{u} =\mathrm{ }0$
We have 
$\mathrm{a}=\frac{\mathrm{v}}{\mathrm{t}}$
$\Rightarrow \mathrm{a}=\frac{400}{1} \mathrm{m}/{\mathrm{s}}^2\mathrm{ }$
Using Newton's second law, we have 
$\mathrm{F}=\mathrm{ma}$, 

where F represents the force
$\Rightarrow \mathrm{F} =0.05\times 400$
$\Rightarrow \mathrm{F}=20 \mathrm{N}$