A 25-tons freight car ran into another freight car of the same mass. The first moves at 2.7 m/s and the second moved towards the first at the speed 0.5 m/s. If the cars were coupled
together after the collision, what was their final speed?

Viscosity - resistance to flow.

Magma has a higher viscosity if it has a lower temperature, is rich in silica, and contains a high abundance of dissolved gases.

Explanation:

Viscosity is referred to as a fluid's (liquid or gas) opposition or resistance to flow or change in shape. This resistance to motion or flow is caused by the internal friction between the molecules in the fluid. Viscosity denotes the thickness of the fluid. With increasing temperature, the viscosity decreases (thins) while with decreasing temperature, the viscosity increases (thickens).

Magma is a mixture of molten or liquid rock, crystals, dissolved gases, etc formed deep inside the earth and it causes volcanic eruptions when expelled onto the Earth's surface. The chemical composition of magma mostly contains silica, SiO2 (50 to 75% ) and iron, magnesium, sodium, potassium, and calcium form the rest. The magma contains dissolved gases and they give magmas their explosive behavior. The gas composition in magma consists of mostly water vapor and some carbon dioxide and traces of fluorine, sulfur and chlorine gases.

The viscosity of magma depends on the temperature, the composition of the magma and the amount of dissolved gases. As the SiO2 concentration in the magma increases, the viscosity also increases. The presence of a high amount of dissolved gases in magma also increases its viscosity. As the temperature of the magma increases, the viscosity decreases.

The rhyolitic type magma has a higher viscosity than the basaltic type magma and the andesitic type magma as it has a low temperature, rich in silica and contains a high abundance of dissolved gases.