Forces in Fluids Practice Problems
1. A 3000 N car is raised by a 2.5 m3 piston of a hydraulic lift. If 250 N was applied to the small
piston of this lift, what is the area of the small piston?
2. A 35 N force applied to a 0.50 m3 piston will lift a 430 N block. What is the area of the piston
that lifts the block?
3. When 445 Pa of pressure is applied to the large piston of a hydraulic lift, a 7700 N truck can be
raised. What is the area of the piston raising the truck?
4. A 650 kg rock displaces 28 m3 of water when placed in a freshwater lake. Use forces to
demonstrate whether this rock will float or sink in freshwater.
5. A 200 m3 balloon has a mass of 980 kg. Will this balloon float or sink in air (density = 1.2041
kg/m3)? Use forces to support your answer.
6. An object with a mass of 45 kg displaces a volume of 140 m3 when placed in a fluid. If the mass
of the fluid displaced is 1.27 x 105 kg, what is the density of the fluid? What is the density of the
object? What is the buoyant force acting on the object? What is the object’s weight?
7. A submarine is at a depth of 310 meters under the ocean’s surface. What pressure does the
submarine experience at this depth?
8. A space probe sinks 40 m into a fluid on a distant planet. If the atmospheric pressure at sea
level on the planet is twice that of Earth’s, the acceleration due to gravity is 13.6 m/s2 and the
probe experiences at 40 m is 1.4 x 108 Pa, what is the density of the fluid?
9. If a fish is subjected to a pressure of 1.75 x 105 when it is swimming in a freshwater lake. At
what depth is the fish swimming?
Answers
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0.21 m3
6.1 m3
17.3 m3
Fg = 6.4 x 103 N; Fb = 2.7 x 105 N; float
Fg = 9.6 x 103 N; Fb = 2.4 x 103 N; sink
density of fluid = 907 kg/ m3; density of object = 0.32 kg/ m3; Fb = 1.25 x 106 N; Fg = 442 N
P = 3.2 x 106 Pa
Density of fluid = 2.6 x 105 kg/ m3
Depth = 7.5 m