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Problem Set 4

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MECH 331 Fluid Mechanics

Problem Set No. 4

1. In the figure, the 8-ft diameter cylinder weighs 500lb and


rests on the bottom of a tank that is 3-ft long. Water and oil
(s = 0.75) are poured into the left and right portions of the
tanks to a depth of 2ft and 4ft, respectively. Find the
magnitude and direction of the horizontal and vertical
forces needed to keep the cylinder touching the tank at B.

2. Gate AB in the figure (below left) is a quarter circle having a


2-meter radius and is 2.5 meters wide. Find the force F just sufficient to prevent rotation
about hinge B, if weight of gate is 800N.

3. Find the horizontal and vertical forces per foot of width on the Tainter gate shown
(above right).

4. The closed tank in figure (below left) contains oil with a specific gravity of 0.90. The top
surface of the tank contains a 2-m diameter hemispherical dome. If the pressure gage
reads 50 kPa, find the net pressure force acting on the dome.

5. An 18-inch diameter opening in the bottom of a closed


tank is plugged with a 40° cone as shown (above
right). If the air at the top of the tank is pressurized to 2 psi gage, what minimum force Q
is required to hold the cone in position?
6. A 48-inch diameter steel pipe, ¼ -in thick, carries oil of s.g. = 0.822 under a head of 400
ft oil. Compute the (a) stress in the steel, and (b) thickness of steel required to carry a
pressure of 250 psi with an allowable stress of 18,000 psi.

7. A cylindrical container 2.5-m high and 1.0 m in diameter is reinforced with two hoops
300 mm from each end. When it is filled with water, what is the tension in each hoop?

8. Find the specific gravity of the homogenous solid


body that floats in two liquids as shown (left). The body
consist of a 1-ft diameter hemisphere and a 1-ft diameter
by 3-ft long
cylinder.

9. A hollow
cube 1.0m on
each side weighs
2.4 kN. The cube
is tied to a solid
concrete block
weighing 10.0 kN. Will these two objects sink in
water?

10. A 2-ft diameter floating cylinder is connected to


a cord that pulls on the top end of a 5-ft wide
rectangular gate, as shown (right. The cylinder is
to have a weight in air that causes the gate to
open when the water height (h) falls below 6 ft.
Find the weight of the cylinder.

11. Each of the two spheres shown below is made of a material having a specific gravity of
1.5. If the system is in equilibrium, determine the diameter D of the sphere that is
completely submerged in the water of the open tank.
12. To make the 1-ft long, 3-inch diameter wood cylinder stable in the vertical position, a
0.30-inch long lead cylinder with the same diameter is rigidly attached to the bottom of
the wood cylinder and the system is placed in water as shown below. If the specific
gravity of wood is 0.50 and lead is 11.3 respectively:
a. Find the equilibrium position of the wood-lead cylinder by calculating the value
of H (height of cylinder protruding from water surface).
b. Is the wood-lead cylinder stable in this vertical position?

13. A barge weighing 1,500 kN has the horizontal cross section at the waterline shown
below. The center of buoyancy 2 meters below the water level, and the center of gravity
is 500 mm below the water level. Calculate the value of the metacentric height.

14. Determine the metacentric height of the torus (doughnut shape) shown below. One half
of the torus lies above the water surface.

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