How to solve Dynamics/Forces problems

Process

  1. Draw a diagram of the problem, labeling a few quantities
  2. Create a free body diagram with the main forces (IMPORTANT) and define your axes. A good set up is positive in the direction of acceleration.
    1. Create a FBD with the component (optional)
  3. Create your \(F = ma\) equation with individual axes (one for the x-axis, one for the y-axis), keeping in mind the signs. Remember that some forces only have a component acting in a given axis.
    1. Don’t group up forces in the same direction (ex: \(mg-(\mu N + T) = ma\))as you may forget to distribute the sign. Instead, individually assign each force a sign (ex: \(mg-\mu N - T = ma\))
  4. Substitute the known expressions for the quantities that have them (\(F_g=mg, f=\mu N\); etc)
  5. Solve for the necessary quantities. You may need to solve both equations or only one.

Misc. Tips