Answer: 91.94 kg
Explanation: Supoose Al's mass is m. The combined mass is 168kg, so Jo's mass is 168 - m.
The Law of Conservation of Momentum states that when two objects collide, the total momentum of both objects before the collision is the same as the total momentum of both objects after the collision.
At the beginning, Al and Jo are united without movement, so their initial momentum is zero.
After the release of their hands, Al goes in one direction and Jo moves to the opposite direction. Suppose the direction Al is moving is positive. Conservation of momentum will be

where
index i referes to initial momentum
index f to final momentum
index 1 refers to Al
index 2 to Jo
Calculating:
![m(0.91)-[(168-m)(1.1)]=0](https://tex.z-dn.net/?f=m%280.91%29-%5B%28168-m%29%281.1%29%5D%3D0)


m = 91.94
Al has a mass of 91.94 kg.
Farmula 2gh=vf²-vi²
2×0.42×9.81=0²-vi²
8.2404=vi²
Vi=✓8.2404
Vi=2.87m/sec
The volume of water that is displaced by the crown is equal to the volume of the crown so by measuring the displaced water volume one can simply determine the density of the crown which is it's mass divided by its volume. if it's not equal to 19.32 per cubic centimeters (which is the density of the pure gold) we can conclude that it has impurities