A toy rocket of mass 0.1 kg hass a small fuel of mass 0.02 kg, which it burns out in 3s. Starting from rest on a horizontal smooth track, it gets a speed of `20ms^(-1)` after the fuel is burnt out. What is the approcimate thrust of the rocket ? What is the energy content per unit mass of the fuel ? (Ignore the small mass variation of teh rocket during fuel burning).

Explanation

Here,
mass of toy rocket, `m_(1)=0.1kg,`
mass of fuel, `m_(2)=0.02kg , t=3s`
initial velocity `u=0`
finial velocity `u=20m//s`
From `u=u+at`
`20=0+axx3,a=(20)/(3)ms^(-2)`
Thrust on the rocket, `F=m_(1)a`
`=0.1xx(20)/(3)=(2)/(3)N`
If s is the distance moved by the rocket in 3 sec, then from
`s=ut+(1)/(2)at^(2)=0+(1)/(2)xx(20)/(3)xx3xx3=3-m.`
Energy content of the fuel
`=` Work done on rocket
`=` Thrust `xx` distance
`=(2)/(3)xx30=20J`
Energy content per unit mass of the fuel
`=(20)/(0.02)=1000 "joule"//kg`