Monday 25 Oct

Turn in Test Justifications & Lab write-up ("Bob" on a string)

Quiz on Free Response Tomorrow

1. What is the absolute pressure at a location 20.0 m below the surface of the sea?  (The density of seawater is 1.03 X 10³ kg/m³) (P_atm = 1.0 x 10⁵ Pa)

1. P_absol = (Depth)(Density)(g) + P_atm

   _{= (20)(1030)(10)  +}  1.0 x 10⁵ Pa

      ₌   3.1 x 10⁵ Pa

2. You are at 20.0 m beneath the surface of a sea.  Then you dive to 45.0 m beneath the surface, what happens to the absolute pressure on you? (more than doubles or less than doubles)

2. less than doubles

 _{Press at 20m =}  3.1 x 10⁵ Pa

_{Press at 45m = (45)(1030)(10)  +}  1.0 x 10⁵ Pa

      ₌   5.6 x 10⁵ Pa

3. A 1.0 m³ object floats in water with 60% of it below the waterline.  What does the object weigh out of the water (r_water = 1000kg/m³)?

3.  Weight = Mg

      mass = (.6m³)(1000kg/m³) = (600kg)

      W = (600kg)(10N/kg)  = 6,000N

4.

a) A dam that has a water lever of 120m high has a pipe at the bottom that sends the water to a turbine. What is the speed of the water as it goes through the pipe (assume that there is no back pressure on the water slowing it down as it is leaving the pipe)?

b) What is the flow rate if the cross section area of the pipe is 2.0m²?

c) What is the volume that leaves the dam in 3 mins?

4. a) mgh = 1/2mv²

     ^{v = √(2gh) = √(2)(10)(120)}

     ^{v = √(2,400) = 50m/s}

b) Flow rate = Volume/time = (Velocity)(area)

 (vA) = (50m/s)(2.0m²) = 100 m³/s

c) Flow rate = Volume/time

          100 m³/s  = Volume/180s

          Volume = (100 m³/s)(180s) = (18,000m³)