Given :m1=1kg, m2=5kg, u1=10ms⁻¹, u2=0
Momentum of the system just before collision, Pi=m1u1+m2u2
Pi=1×10+5×0=10 kgms⁻¹
Mass of the combined object, M=m1+m2=6kg
Let velocity of combined object be v
According to conservation of momentum, momentum of the system just after the collision, Pf=Pi ⇒Pf=10 kg m s⁻¹
Mv=10
or, 6×v=10
or, v=1.67 m/s