Total mass of h2o2 in 20 grams of an aqueous h2o2 solution

3=  (x/20.0g) x 100%

or    (20)(0.03)

Answer  0.6g

d.) circle motion requires a force to give it a centripetal acceleration.

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.