An explosion breaks a rock into three parts in a horizontal plane. Two of them go off at right angles to each other. The first part of mass 1 kg moves with a speed of 12 ms-1 and the second part of mass 2kg moves with 8 ms-1 speed. If the third part flies off with 4 ms-1 speed, then its mass is
(b) We have p1+p2+p3=0 [∴ P=mv]
∴ 1x12i+2x8j+p3=0
=> 12i+16j+p3=0
=> p2=-(12i+16j)
p3=√(12)2+(16)2=144+256=20 kg-m/s
Now, p3=m3v3
=> m3=p3/v3=20/4=5kg