Question 41. A water sample has a pH of 9.25. The concentration of hydroxyl ions in the water sample is

Question 42. A town is required to treat 4.2 m3/min of raw water for daily domestic supply. Flocculating particles are to be produced by chemical coagulation. A column analysis indicated that an overflow rate of 0.2 mm/s will produce satisfactory particle removal in a settling basin at a depth of 3.5 m. The required surface area (in m2) for settling is

Question 43. The horizontal distance between two stations P and Q is 100 m. The vertical angles from P and Q to the top of a vertical tower at T are 3o and 5o above horizontal, respectively. The vertical angles from P and Q to the base of the tower are 0.1o and 0.5o below horizontal, respectively. Stations P, Q and the tower are in the same vertical plane with P and Q being on the same side of T. Neglecting earth's curvature and atmospheric refraction, the height (in m) of the tower is

Question 44. A two-lane urban road with one-way traffic has a maximum capacity of 1800 vehicles/hour. Under the jam condition, the average length occupied by the vehicles is 5.0 m. The speed versus density relationship is linear. For a traffic volume of 1000 vehicles/hour, the density (in vehicles/km) is

Question 45. A 2 km long pipe of 0.2 m diameter connects two reservoirs. The difference between water levels
in the reservoirs is 8 m. The Darcy-Weisbach friction factor of the pipe is 0.04. Accounting for
frictional, entry and exit losses, the velocity in the pipe (in m/s) is:

Question 46. The transplantation of rice requires 10 days and total depth of water required during transplantation is 48 cm. During transplantation, there is an effective rainfall (useful for irrigation) of 8 cm. The duty of irrigation water (in hectares/cumec) is:

Question 47. The normal depth in a wide rectangular channel is increased by 10%. The percentage increase in the discharge in the channel is:

Question 48. A settling tank in a water treatment plant is designed for a surface overflow rate of 30 m3/day.m2. Assume specific gravity of sediment particles = 2.65, density of water (ρ) = 1000 kg/m3, dynamic viscosity of water (μ) = 0.001 N.s/m2, and Stokes' law is valid. The approximate minimum size of particles that would be completely removed is:

Question 49. The percent voids in mineral aggregate (VMA) and percent air voids (Vv) in a compacted cylindrical bituminous mix specimen are 15 and 4.5 respectively. The percent voids filled with bitumen (VFB) for this specimen is:

Question 50. A student began experiment for determination of 5-day, 20°C BOD on Monday. Since the 5th day fell on Saturday, the final DO readings were taken on next Monday. On calculation, BOD (i.e. 7 day, 20°C) was found to be 150 mg/L. What would be the 5-day, 20°C BOD (in mg/L)? Assume value of BOD rate constant (k) at standard temperature of 20°C as 0.23/day (base e). __________