Newton's Laws Legacy Problem #2 Guided Solution
Problem*
About twenty percent of the National Football League weighs more than 300 pounds. At this weight, their Body Mass Index (BMI) places them at Grade 2 obesity, which is one step below morbid obesity. Determine the mass of a 300 pound (1330 N) football player.
Audio Guided Solution
Here we're asked to find the mass of a 300-pound, or a 1330-newton, football player. Using my conceptual understanding of terms, I know right away that what they're giving me is they're giving me the weight of a football player. The 1330 newtons is the weight, and I know it's the weight because I observed the unit N for newtons, and I know that we measure weight in units of newtons. After all, it's a force, a force of gravity, and forces are measured in newtons. What I'm asked to calculate here is I'm asked to calculate the mass of the football player in kilograms. So I need to find an equation that relates the weight and the mass, and that equation is that the weight equal mass times g, where g is 9.8 newtons per kilogram, or 9.8 meters per second per second. So to determine the mass, I need to take the weight in newtons and divide it by the value of g. Doing that will give me the value of mass in kilograms, and that's what I'm being asked for.
Solution
136 kg
Habbits of an Effective Problem Solver
- Read the problem carefully and develop a mental picture of the physical situation. If necessary, sketch a simple diagram of the physical situation to help you visualize it.
- Identify the known and unknown quantities in an organized manner. Equate given values to the symbols used to represent the corresponding quantity - e.g., \(v_o = \units{0}{\unitfrac{m}{s}}\); \(a = \units{4.2}{\unitfrac{m}{s^2}}\); \(v_f = \units{22.9}{\unitfrac{m}{s}}\); \(d = \colorbox{gray}{Unknown}\).
- Use physics formulas and conceptual reasoning to plot a strategy for solving for the unknown quantity.
- Identify the appropriate formula(s) to use.
- Perform substitutions and algebraic manipulations in order to solve for the unknown quantity.
Read About It!
Get more information on the topic of Newton's Laws at The Physics Classroom Tutorial.