Newton's Laws Legacy Problem #4 Guided Solution

I'm always intrigued by the idea that many students have that being a good problem solver simply involves having good math skills. Well, for certain, being a good problem solver does involve math skills, but it involves so much more than simply math skills. One thing that is critical to being a good problem solver is having a solid conceptual understanding of terms and being a good reader. Here we're told that we have an 86-kilogram man, and we presume that that's the mass of the man on Earth, or ask, what's the mass and what's the weight on the moon, where the gravitational field is one-sixth that of the Earth? Now, to do this problem, you don't need good math skills. You need good conceptual understanding of physics. You need to understand what they've given you and what they're asking you. And what they've given you is the mass of a man on Earth. And one of the things they're asking you is the mass of the same man on the moon. So to get this right, you don't need good math skills. In fact, math skills will get in your way. What you need is solid understanding of concepts. And one of the big concepts here is that the mass of a person or any object is independent of its location in the universe. It's the same on Earth as it is on the moon. So the mass of this man on the moon is 86 kilograms. It simply refers to the amount of stuff that's present in the thing. Even if you take the thing to the moon, it's still got the same stuff in it. And it thus still has the same mass of 86 kilograms. Now, the other part of this problem is determining the weight of this 86-kilogram man on the moon. And so now you have to read and interpret what it means when they say the gravitational field is one-sixth that of the Earth. What they mean by that is the value of G, the gravitational field strength, is one-sixth of the 9.8 value that it is on Earth. Now, you could calculate that if you wanted, and you're going to eventually need to. But do understand that what they're telling you is gravity pulls on any kilogram of mass on the moon with one-sixth the amount of force as it does upon the Earth, which would explain why we measure the value of G oftentimes in units of newtons per kilogram. So to find the weight of the man on Earth, two things you could do. You could take the 9.8 and divide it by 6 to get the new value of G, the G value for the moon, and then multiply by the mass of 86 kilograms. Or you could simply find the man's weight on Earth, 86 times 9.8, and then know that on the moon it's one-sixth that value.