1.A 20 cubic meter tank contains ultimate BOD at a concentration of 550 mg/L. If the BOD reaction rate constant is -0.42/day, what is the concentration of BOD remaining after 3.0 days?
2.Consider a cylindrical copper wire 3.0mm in diameter and 3x10^4 mm long. calculate its elongation when a load of 100N is applied. Assume that the deformation is totally elastic and its Young Modulus is 110GPa. Express your answer in [mm] to 2 decimal places.
3.A direct shear cell 25.4cm x 25.4 cm in plan is filled with dry sand. a normal load of 6kN is applied to the sample, and the shear failure is 3.5kN. What is the anle of internal friction for the sand?