COMEDK Exam 2014 Solved Paper

Given, mass of shell, ms=20g=0.02kg
Mass of gun, mg=100kg
Speed of shell, vs=80m∕s
Let vg be the speed of the recoil of gun, then according to law of conservation of linear momentum.
Total initial momentum = Total final momentum
⇒ 0=msvs+mgvg
⇒ 0=0.02×80+100vg
⇒ 0=1.6+100vg
⇒ vg=

−1.6

100

=−1.6×10−2m∕s=−1.6cm∕s
Negative sign indicates that gun moves in opposite direction to that of shell.
∴ Speed of recoil of gum =1.6cm∕s