Last newsletter contained two rather 'physics' oriented questions, one dealing with scrap iron on a barge and the other dealing with momentum and energy as related to a snow sled.
For the scrap iron on the barge, the water level would go down. When the iron is on the barge, the barge displaces a volume of water equivalent to the mass of the iron (Archimedes' principle). If the iron falls into the water, the iron will then displace a volume of water equivalent to its own volume. Since the density of iron is greater than that of water, less water will be displaced and the water level will drop.
For the snow sled scenario, the Momentum method is correct and the Energy method is wrong. Remember in an inelastic collision Momentum is conserved but Kinetic energy is not. This is because the internal forces between the colliding objects do work and therefore convert Kinetic Energy into heat. Because the internal forces are always acting in equal and opposite pairs they have no effect on the total momentum.
In this case the snow collides with the sled and the internal forces accelerate the snow from rest in the horizontal direction to the speed of the sled.