Problem 2.8 Suppose that F₂ = 6 kN. (Figure 1) Part A Determine the directions of the force F₂ components acting along the u and vaxes. along the negative u axis and along the negative v axis along the positive u axis and along the positive v axis along the negative u axis and along the positive v axis along the positive u axis and along the negative u axis Submit My Answers Give Up Figure 1 of 1 75° V 30° 30° F₁ = 4 kN F2 Part B Determine the magnitude of the component (F2)μ- Express your answer with the appropriate units. Part C ? Units My Answers Give Up (F2). Value Submit Incorrect; Try Again; 5 attempts remaining Determine the magnitude of the component (F2), Express your answer with the appropriate units. ? u (F2), Value Units Submit My Answers Give Up

A current problem in the U.S. Air Force is the neck/shoulder fatigue experienced by pilots. To be able to fly missions at night, the pilots wear night vision goggles, which are attached to the front of the helmet. Unfortunately, these are heavy, causing a large downward torque of the head, which must be counteracted by the neck muscles, which then fatigue. To alleviate this problem, many pilots have started attaching random lead weights to the back of the helmet. Find the appropriate weight that would best balance the head and minimize neck fatigue – You must show your free body diagram. Assumptions: a) center of gravity of goggles is 20 cm in front of neck pivot point, b) load of goggles1.0 kg mass, c) center of gravity of lead weight is 10 cm behind neck pivot point, d) load of bare helmet 3 kg mass, e) center of gravity of helmet is 2 cm in front of neck pivot, f) load of head 4.0 kg mass, and g) center of gravity of head is right at neck pivot point.  Answer: ___________________

(5.1) Show that o, +o,(=0 +0,) is a conserved quantity through rotation of coordinates. We still assume a 2D medium. (5.2) What is the maximum shear stress in the medium if the principal stresses are given by o, and o, ?

SECTION B- STRUCTURES-DR LARISA MALYSHEVA QB1 DIRECT STRESS Two round solid bars of different materials are connected (in parallel) and have a common tensile force, P, of 190 kN is applied,ras shown in Figure QB1. For each bar, determine the: a) b) Stress. Strain and Strain in the diameter. Use the following information. Clearly show all your derivations. The original length of each bar = 1.7m. %3D Steel Bar: 32mm Dia. Poisson's Ratio = 0.31 18mm Dia. Young's Modulus = 210 GPa %3D Steel Aluminium Bar Bar Common Connection Aluminium Bar: P = 190 kN Poisson's Ratio = 0.34 Young's Modulus = 68 GPa Fig QB1