1. Tightening the loose ends Physics 11-3-14
Forces at an Angle
Tightening the loose ends
Physics

2. Today’s goal – remediate issues from quiz
Go over quiz as a class
In table groups (i.e. new groups), work through guided practice on the whiteboard for the items we had trouble with.

3. Go over quiz as a class

4. Concepts we did well on Vector terminology (6-9)
Resolving a vector into x and y components (1)
Adding vectors using the Pythagorean theorem (2,10)
Relative velocity (10)

5. Concepts we need to practice
Determining when to use
Fnet=ma vs
Fnet=sum of all the forces acting in that plane
Specific problem types
Applied forces at an angle, horizontal surface (3)
Forces on an incline (5)
Tension at an angle (4)

6. How do you know which equation to use?

7. Forces at an angle example
An object in equilibrium has three forces exerted on it. A 33.0N force acts at 90.0 degrees from the x-axis and a 44.0N force acts at 60.0 degrees from the x-axis. What are the magnitude and direction of the third force?
74.4N, 253 degrees

8. Forces on an incline example
If the coefficient of kinetic friction between the ground a boulder and the mountainside is 0.40, the mass of the boulder is 20 kg, and the slope of the mountain is a constant 30 degrees, what is the force that a person must apply to the boulder to move it up the mountain at constant velocity?
166N

9. Tension at an angle
Joe wishes to hang a sign weighing 750 N so that cable A, attached to the store, makes a 30.0 degree angle. Cable B is horizontal and attached to an adjoining building. What is the tension in cable B?
435N, right

10. Problem set practice - forces