Chapter 15, Problem 15.10P

2-7 The force P applied at joint D of the square frame causes the frame to sway and form the dashed rhombus. Determine the average normal strain developed in wire AC. Assume the three rods are rigid. I understand how you calculate length LAC its just the sqrt(400^2+400^2) = 565.685mm. I do understand that you have to take LAC'-LAC/LAC to get .0258mm/mm. I'm just not understanding the cosine law used to calculate LAC'. I guess what I'm asking is why do you use cos instead of sin or tangent? I've been trying to understand why that was used for a bit now and it's probably something simple I'm forgetting. If you can, please clarify it in detail. Thank you so much!

Traffic flow on a three-lane (one direction) freeway can be described by the Greenshields model. One lane of the three lanes on a section of this freeway will have to be closed to undertake an emergency bridge repair that is expected to take 2 hours. It is estimated that the capacity at the work zone will be reduced by 30 percent of that of the section just upstream of the work zone. The mean free flow speed of the highway is 70 mi/h and the jam density is 150 veh/mi/In. If it is estimated that the demand flow on the highway during the emergency repairs is 85 percent of the capacity, using the deterministic approach, determine the following. (a) the maximum queue length (in veh) that will be formed veh (b) the total delay (in h) h (c) the number of vehicles that will be affected by the incident veh (d) the average individual delay (in min) min

Non-constant sections are used in bridges without changing the appearance of the bridge significantly. Refer to the figure below. Compute the ratio of moment inertial after to before of the plate girder shown (greater than 1). A 10x0.5" steel plate of the same grade as the plate girder and is fillet welded to the flanges