This happens just because of density...because the sheet has high density and the box has low density.due to air trapped in the box.That's why the sheet shink in water and the box remain float.That's it.

Why does a 1/2 kg sheet of tin sink in water but float when converted into a box or boat?

Introduction:
The behavior of objects in water depends on their density and shape. A 1/2 kg sheet of tin sinks in water due to its density, but when the same sheet is transformed into a box or boat, it floats. This phenomenon can be explained by considering the concepts of buoyancy, density, and Archimedes' principle.

Density and Buoyancy:
Density is a physical property that describes the mass of an object per unit volume. If the density of an object is greater than the density of the fluid it is immersed in (in this case, water), the object will sink. Conversely, if the object's density is less than the fluid's density, it will float.

Archimedes' Principle:
Archimedes' principle states that when an object is immersed in a fluid, it experiences an upward buoyant force equal to the weight of the fluid it displaces. This buoyant force opposes the force of gravity acting on the object, causing it to either sink or float.

Explanation:
When the 1/2 kg sheet of tin is in its original form, it has a relatively high density. Its mass is concentrated in a small volume, resulting in a high mass-to-volume ratio. As a result, the density of the sheet is greater than that of water, causing it to sink.

However, when the same sheet is transformed into a box or boat, its shape changes. The sheet now displaces a larger volume of water compared to its original form. This increased volume of water displaced creates a greater buoyant force according to Archimedes' principle. The buoyant force acts in the opposite direction to the force of gravity, effectively reducing the net downward force on the object.

Effect of Shape:
The shape of an object plays a crucial role in determining its ability to float. By converting the sheet of tin into a box or boat shape, the object's overall volume increases while its mass remains the same. This results in a decrease in the object's density. As the density of the object becomes less than that of water, the buoyant force becomes greater than the force of gravity, allowing the box or boat to float on the water's surface.

Conclusion:
The sinking or floating behavior of objects in water is determined by their density and shape. A 1/2 kg sheet of tin sinks in water due to its high density, but when converted into a box or boat shape, its density decreases and the resulting buoyant force enables it to float. Understanding the principles of buoyancy, density, and the effect of shape helps explain this phenomenon.