A 3.8 kg fish swimming 1.3 m/s swallows an absent minded 1.4 kg fish swimming toward it at a velocity that brings both fish to a halt immediately after lunch. What is the velocity v of the smaller fish before lunch?

Answer 1

The momenta of the two fish before "lunch" must be equal and opposite in order for the final momenum fo be zero. If v is the unknown velocity,
3.8*1.3 + 1.4*v = 0

v = -(3.8*1.3)/1.4 = __

Answer 2

-3.52857