The newton being a unit was never "discovered". It is also a derived unit so it really has no establishing date.
82,12127465
31 kilonewtons (kN) is 3,161.1kg or 6,969.1 pounds.
0.009807 kN
22kN is 2,243.4kg
15kN is 1,529.6kg
2500kg is 24.517kN
16kN is 3,596.9 pounds.
13.5kN is 1,376.6kg
1ton=.1kilo newton
2.0kN is 203.94kg
Newtons or kilonewtons.
3.673kg is 0.036kN (rounded).