Question

mass of gun in this question

Answer 1

m1v1=m2v2
m1=0.05kg v1=30m/s v2 =1m/s m2=?
therefore
m2=30×0.05=1.5kg
1.5 kg mass of gun

Answer 2

use the concept of conservation of linear Momemtum .
because external force equal = 0
so, inital momentum = final momentum

mass of bullet ( m) = 50 g
initial velocity of bullet ( Vb) = 30 m/s (forward)
final velocity of bullet = 0
inital velocity of gun = 0
final velocity of gun (Vg) = 1 m/s (backward)
mass of gun (M ) = ?

inital momentum = mVb + M × 0
final momentum = m× 0 + MVg

hence,
mVb = MVg
50g × 30 m/s = M × 1 m/s
M = 1500 g = 1.5 Kg

hence, mass of gun = 1.5 Kg