5 Displacement and Force in Two Dimensions 3 Forces in Two Dimensions

Transcription

1 5 Displacement and Force in Two Dimensions 3 Forces in Two Dimensions 3(F), 4(C), 4(D), 4(E) MAINIDEA Write the Main Idea for this section. REVIEW VOCABULARY equilibrium Recall and write the definition of the Review Vocabulary term. equilibrium NEW VOCABULARY equilibrant Use your book to define each term. equilibrant 83

2 Student Edition, pp Explain what must be true for an object to be in equilibrium. Refer to Figure 14 and Figure 15 in your textbook, and explain the relationship between the forces acting on the ring in the vector diagrams. GET IT? Identify the relationship between the equilibrant and the resultant vector. Draw a vector diagram below that shows a net force of zero acting on an object. Use four vectors in your drawing. 84

3 Student Edition, pp Identify the system in the problem illustrated in Figure 17. Then describe the factors involved in the first step of solving the problem. Identify the factors involved in choosing the coordinate system for solving the problem described in Figure 17. Identify the force described in Figure 17 that has both x- and y-vector components that must be used to solve the problem. GET IT? Explain why you would choose the x-direction to be parallel to the slope of an inclined plane. 85

4 Student Edition, p. 140 Use with Example Problem 6. Use this column for scratch work and sketches. TRY IT! Problem SLIDE Afrin, who has a mass of 35 kg, is going down a slide sloped at 29. The coefficient of kinetic friction is How fast does she slide 1.5 s after starting from rest? 1. ANALYZE AND SKETCH THE PROBLEM KNOWNS UNKNOWNS m = ϕ = =? μ k = v i = =? μ k = =? 2. SOLVE FOR THE UNKNOWNS Find the angle of F g from the +x-axis: Add forces in the y-direction to write an equation for F N. Use the net force in the x-direction and Newton s second law to solve for a. Because v i, a, and t are all known, use the relationship between velocity, acceleration, and time. 86

5 Student Edition, p. 140 TRY IT! (CONTINUED) 3. EVALUATE THE ANSWER Are the units correct? Is the magnitude of the velocity realistic? SUMMARIZE How does the MAINIDEA for this section relate to the chapter s BIGIDEA? REVIEW IT! 41. MAINIDEA A rope pulls a 63-kg water skier up a 14.0 incline with a tension of 512 N. The coefficient of kinetic friction between the skier and the ramp is Find the magnitude and direction of the skier s acceleration. 42. Forces One way to get a car unstuck is to tie one end of a strong rope to the car and the other end to a tree, then pull the rope at its midpoint at right angles to the rope. Draw a free-body diagram and explain how even a small force on the rope can exert a large force on the car. 87

6 43. Mass A scoreboard is suspended from an arena s ceiling by ten cables. Six of the cables make an 8.0 angle with the vertical while the other four make a 10.0 angle. The tension in each cable is 1300 N. Find the scoreboard s mass? 44. Vector Addition What is the sum of three vectors that, when placed tip to tail, form a triangle? If these vectors represent forces on an object, what does this imply about the object? Describe the motion resulting from these three forces acting on the object. 45. Equilibrium You are hanging a painting using two lengths of wire. The wires will break if the force is too great. Should you hang the painting as shown in the top or the bottom image of Figure 20? Explain. Figure Vector Addition Can the coefficient of friction ever have a value such that a child would be able to slide up a slide at a constant velocity? Explain why or why not. Assume that no one pushes or pulls on the child. 88