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19-11-14 Getting ready for forces quiz

Today’s assignment from textbook:

p. 110-112: 20, 37, 38, 39, 41 and 51.

What you need to know for tomorrow’s quiz:

  • Use of first five equations in your equation sheet
  • Draw force diagrams
  • Evaluate forces to determine balanced/unbalanced net force
  • Special circumstances/types of problems
    • Solve problems with pulleys (pulleys change direction of tension, not magnitude)
    • Solve problems with ramps
  • Solve problems with forces at angles
    • Break down forces into x and y components
    • Solve triangle math using SOHCAHTOA and law of sines

Additional resources

You an find instructional/tutorial videos here.

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11/13 Force diagrams: Two solved problems

Force diagrams, or Free Body Diagrams, are sketches we use in physics to show forces applied to an object or system of objects.

Here are a couple of videos I created to help walk you through some complicated problems. I encourage you to pause them as you go through and see if you can determine the ‘next move.’

Problem A

A 13 kg block of wood slides across the floor with constant speed when it is pulled with a horizontal force of 32 N. What is the friction constant, µ, between the wood and the floor?

Problem B

A block is sliding up a wall with a constant velocity, and a force applied upwards at an angle. Here is a sketch:

sketch showing the box on the wall with the unknowns labeled.
As with many AP questions, you are asked to solve for one variable in terms of the others. In this case, your final equation should be in the form F = (an expression that includes m, μ , and θ )