40 kg girl skates at 3.5 m/s on ice toward her 65 kg friend who is standing still, with open arms. As they collide and hold each other, what is the speed of the couple?

After the collison the speed of the couple is v2 = 1.33[m/s].

Explanation:

We need to consider a direct central impact, as the couple remains together after the impact there is no restitution. Therefore impact the perfectly plastic.

Therefore the initial data:

v1 = velocity of the 40 [kg] girl = 3.5[m/s]

m1 = mass of the first girl = 40 [kg]

m2 = mass of the second girl = 65 [kg]

v2 = velocity of the two girls after the collision.

multiply 2kg by latent heat of vap