Given,
Mass of the bullet is mb=25gm=0.025Kg
Initial velocity of bullet ub=100m/s
From the conservation of energy
Initial kinetic energy = 12mbu2b=10100(12mbu2b)+12mbv2b
10 % (Initial kinetic energy) = final kinetic energy
10100(12mbu2b)=12mbv2b
vb=√0.1u2b=√0.1×100=√10ms−1
Hence, final velocity is √10ms−1