# Sir can you explain me this? I did'n understood.

mass of bullet= 10g = 0.01 kg

velocity of bullet= 1.5 m/s

mass of plank= 90g = 0.09kg

Total momentum before collision= mass of plank x velocity

$=0.01\times 1.5+0.09\times 0=0.015kg\frac{m}{s}$

Total momentum after collision = (mass of bullet +mass of plank)x velocity

$=0.1kg\times V=0.1Vkg\frac{m}{s}$

According to law of conservation of momentum,

Total momentum before collision=Total momentum after collision

$0.015kg\frac{m}{s}=0.1Vkg\frac{m}{s}$

velocity acquired by the plank and the bullet = $0.15\frac{m}{s}$

Regards

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