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Ch 12: Fluid Mechanics
Chapter 12, Problem 12

Hydraulic Lift II.The piston of a hydraulic automobile lift is 0.30 m in diameter. What gauge pressure, in pascals, is required to lift a car with a mass of 1200 kg? Also express this pressure in atmospheres.

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1
Calculate the force needed to lift the car using the formula F = m imes g, where m is the mass of the car and g is the acceleration due to gravity (approximately 9.8 m/s^2).
Determine the area of the piston using the formula A = \pi \times r^2, where r is the radius of the piston. Convert the diameter to radius by dividing it by 2.
Calculate the required gauge pressure using the formula P = \frac{F}{A}, where F is the force calculated in step 1 and A is the area of the piston calculated in step 2.
Convert the gauge pressure from pascals to atmospheres using the conversion factor 1 atm = 101325 Pa.
Summarize the results by stating the gauge pressure in both pascals and atmospheres.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hydraulic Systems

Hydraulic systems utilize incompressible fluids to transmit force. According to Pascal's principle, a change in pressure applied to an enclosed fluid is transmitted undiminished throughout the fluid. This principle is fundamental in hydraulic lifts, where a small force applied on a small piston generates a larger force on a larger piston, allowing heavy objects to be lifted with relative ease.
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Pressure Calculation

Pressure is defined as force per unit area, typically measured in pascals (Pa) in the SI system. To calculate the pressure required to lift an object, one must first determine the weight of the object (mass times gravitational acceleration) and then divide this force by the area of the piston. This relationship is crucial for determining the gauge pressure needed in hydraulic systems.
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Conversion of Units

In physics, it is often necessary to convert between different units of measurement. For pressure, the conversion from pascals to atmospheres involves knowing that 1 atmosphere is equivalent to 101,325 pascals. Understanding how to perform these conversions is essential for accurately interpreting and communicating results in various contexts, such as engineering and physics problems.
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Related Practice
Textbook Question
A square steel plate is 10.0 cm on a side and 0.500 cm thick. (a) Find the shear strain that results if a force of magnitude 9.0×10^5 N is applied to each of the four sides, parallel to the side. (b) Find the displacement x (in centimeters).
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Textbook Question
A brass wire is to withstand a tensile force of 350 N without breaking. What minimum diameter must the wire have?
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Textbook Question
Two circular rods, one steel and the other copper, are joined end to end. Each rod is 0.750 m long and 1.50 cm in diameter. The combination is subjected to a tensile force with mag-nitude 4000 N. For each rod, what are (a) the strain and (b) the elongation?
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Textbook Question
A pressure difference of 6.00 * 104 Pa is required to maintain a volume flow rate of 0.800m3/s for a viscous fluid flowing through a section of cylindrical pipe that has radius 0.210 m. What pressure difference is required to maintain the same volume flow rate if the radius of the pipe is decreased to 0.0700 m?
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Textbook Question
A small circular hole 6.00 mm in diameter is cut in the side of a large water tank, 14.0 m below the water level in the tank. The top of the tank is open to the air. Find (a) the speed of efflux of the water and (b) the volume discharged per second.
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Textbook Question
A cubical block of wood, 10.0 cm on a side, floats at the interface between oil and water with its lower surface 1.50 cm below the interface (Fig. E12.33). The density of the oil is 790 kg/m^3. (a) What is the gauge pressure at the upper face of the block? (b) What is the gauge pressure at the lower face of the block? (c) What are the mass and density of the block?

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