Two solid spheres of radius r made of the same type of steel are placed in contact, as shown in the figures above. The magnitude of the gravitational force that they exert on each other is f1. When two other solid spheres of radius 3r made of this steel are placed in contact, what is the magnitude of the gravitational force that they exert on each other?.

It depends on the subject for me. some exams are easier than others so i usually go through it and answer questions i know based on my general knowledge, then double check after. going through the lesson can a lot  because the exams can be  very lesson-specific, but sometimes they are ridiculously long so a lot of people don't take the time. i did find that, when i went through the lessons, i was making 100's on my exams vs strictly using + the internet and  i make 90's. 

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Ok, you asked the question and posted the answer on there. what do you need?