1. Equilibrium Section 7.6, # 83 To view this presentation: Right click on the screen and select “Full Screen”.

2. Section 7.6, # 83 1000 lb 60 o 30 o

3. Identify all the forces that are acting on the object. 1000 lb 60 o 30 o R S Equilibrium R + S + W = 0 W

4. Find the direction of R. 60 o R R = |R|[(cos )i + (sin )j ] 30 o In quadrant II, a 30 o reference angle is 150 o (180 – 30 = 150) R = |R|[(cos 150 o )i + (sin 150 o )j ]

5. 30 o S S = |S|[(cos )i + (sin )j ] 60 o In quadrant I, a 60 o reference angle is 60 0. S = |S|[(cos 60 o )i + (sin 60 o )j ] Find the direction of S.

6. 270 o W W = |W|[(cos )i + (sin )j ] W = |W|[(cos 270 o )i + (sin 270 o )j ] Find the direction of W. Remember, |W| = 1000 W = 1000[(cos 270 o )i + (sin 270 o )j ] and cos 270 o = 0 and sin 270 o = -1 W = -1000j

7. Identify all the forces that are acting on the object. 1000 lb 60 o 30 o R S Equilibrium R + S + W = 0 W R = |R|[(cos 150 o )i + (sin 150 o )j ] S = |S|[(cos 60 o )i + (sin 60 o )j ] W = -1000j cos 150 o = -, sin 150 o = cos 60 o = sin 60 o = cos 270 o = 0 sin 270 o = -1  

8. Identify all the forces that are acting on the object. Equilibrium R + S + W = 0 - |R| + |S| + 0 = 0 cos 150 o = -, sin 150 o = cos 60 o = sin 60 o = cos 270 o = 0 sin 270 o = -1    |R| + |S| + -1000 = 0 

9. Identify all the forces that are acting on the object. Equilibrium R + S + W = 0 - |R| + |S| = 0  |R| + |S| = 1000  |R| + |S| = 0 |R| + |S| = 2000 3|R| - |S| = 0 |R| + |S| = 2000 4|R| = 2000 |R| = 500 lb and |S| = 866 lb 2 2