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41 Chapter 15 Fluids Practice Problems
Fluids  = m/V,
H20= 1..000 x103 kg/m3.
Pressure = Force / Area: P 
W = mg = gV
, P  Patm  mgh , [P]=N/m2 = 1 Pa, 1 atm = 1.01x105 Pa
Mass Flow Rate:  Av, Continuity : A1v1  A2 v2 , Bernoulli: P1   v12   gy1  P2   v22   gy2
Archimedes: Buoyant force is equal to the weight of fluid displaced fluid:
BF: FB   gV , If object   fluid  FLOAT
Archimedes and Buoyancy
1 An oddly shaped solid object is submerged in a cylindrical beaker of water and is found to
displace 0.08m3 of water. a) What is the buoyant force acting on the metal object?
b. The above object weighs 1500 N in air. Will the object float or sink? Why?
2. A cube of material of density 2x103 kg/m3 is suspended in water with its top 3 meters below the surface of
water. The cube measures 0.1 on each side. a) What is the buoyant force on it? b) Now the cube is suspended
by a string that is connected to a scale. What is the apparent weight of the cube?
3. Calculate the velocity to which water can be squirted with the hose with a constant flow rate of 0.500 liters
per second if it :
a) emerges from the hose (r = 0.900cm) without the thumb
b) emerges with the thumb reducing the radius to r = 0.250 cm.
c)What is the maximum height the water can reach if it is shot straight up with the thumb?
4. A swelling in a blood vessel doubles its cross sectional area. By how much will the blood flow change as it
moves through the enlarged area? The speed of blood (density = 1060 kg/m3) through a normal part of the
vessel is v = .5 m/s.
41 Chapter 15 Fluids Practice Problems
5. Water flows at a speed of 20m/s through a tube of cross-sectional area
0.25 m2, as shown at point A. The Pressure at A is 1.8x105 Pa.
a) the tube now runs uphill so that the distance above ground increases by
3.0 m. What is the pressure of the water at point B if we ignore fluid
b) The tube expands to a cross-sectional area of 1.00 m2 at point C. The
average height above ground does not change. What is the speed of the water at point C, Ignoring fluid friction
and assuming that the water speed at point B is 4.0 m/s?
6. Efflux Speed: A large tank is filled with water up to a depth of 15 m above ground. A spout located 10.0 m
above the bottom of the tank is then opened. With what speed will water
emerge from the spout? The tank is so large that the liquid level at the
top changes very slowly.
7. Calculate the approximate force on a square meter of sail, given the horizontal velocity of the wind is 6.00
m/s parallel to its front surface and 3.50 m/s along its back surface.
8. AVenturi Meter is a device for measuring the speed of a fluid in a pipe. Find the mass flow rate and the
speeds v1 an v2 if P2-P1 = 120Pa, A2=0.05m2 and A1 = 0.04m2 and the density of the fluid is 1/38 kg/m3.