The grass on a hill washes away after a heavy rain. The animals that eat the grass leave the area to find food somewhere else. A group of students wants to make the hill the way it was before the rain. They want a solution that will last a long time. They plan to replant the grass
and bring mice from a pet store to live on the hill.
Does their solution meet all of their needs? Choose yes or no and one reason why.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

a gas, having a molecular weight of 13 kg/kmol and a kinematic viscosity of 0.25 cm2/s, flows through a pipe 0.25 m internal diameter and 5 km long at the rate of 0.4 m3/s and is delivered at atmospheric pressure.