The principle of conservation of momentum can be used to find the speed of the truck after loading. Before loading, the momentum of the truck is given by:
p1 = m1 * v1
where m1 is the mass of the truck (1600 kg) and v1 is the speed of the truck (2.5 m/s). After loading, the total mass of the system is the mass of the truck and the load, which is 1600 kg + 3500 kg = 5100 kg. The speed of the truck after loading is given by:
v2 = p1 / (m1 + m2)
where m2 is the mass of the load (3500 kg). Plugging in the values, we get:
v2 = (1600 kg * 2.5 m/s) / (1600 kg + 3500 kg) = 2.23 m/s.
So the speed of the truck immediately after loading is 2.23 m/s.