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Chapter 7 Problem B
1. If you placed a helicopter with a mass of 1.03  103 kg on a large piston of a hydraulic
lift, what force would need to be applied to the small piston in order to slowly lift the
helicopter? Assume that the weight of the helicopter is distributed evenly over the large
piston’s area, which is 1.40  102 m2. The area of the small piston is 0.80 m2.
2. Imagine an agricultural show in which a large goat with a mass of 181 kg exerts a
pressure on a hydraulic-lift piston that is equal to the pressure exerted by three pygmy
goats, each of which has a mass of 16.0 kg. The area of the piston on which the large
goat stands is 1.8 m2. What is the area of the piston on which the pygmy goats stand?
3. The greatest load ever raised had a mass of 4.0  107 kg. Imagine that this load could
have been raised using a single huge hydraulic lift. If the load had been placed on the
large piston and a force of 1.2  104 N had been applied to the small piston, which had
an area of 5.0 m2, what must the large piston’s area have been?
4. Suppose a pressure equal to that estimated for the sun’s interior (2.0  1016 Pa) acts on
a spherical surface within a star. If a force of 1.02 N  1031 N produces this pressure,
what is the area of the surface? What is the sphere’s radius r? (Recall that a sphere’s
surface area equals 4r2.)
5. The surface of the planet Jupiter is believed to consist of liquid hydrogen. Above this
surface lies a thick atmosphere that exerts a pressure of 1.00 x 107 Pa on Jupiter’s
surface. If the total force exerted by this atmosphere is 6.41x1023 N, what is the area of
Jupiter’s surface?
6. In a certain gasoline engine, the ignited gasoline and air mixture in a single cylinder
exert a pressure of 1.50 x 106 Pa on the upper surface of the piston. If the force exerted
by the gas on the piston is 1.22 x 104 N, how large is the area on the piston’s upper
7. The two Echo satellites, which were launched in 1960 and 1964, were early examples of
communications satellites. Suppose the gas pressure inside Echo 1 was the same as
the atmospheric pressure at Earth’s surface. If the total force exerted on the inner
surface of Echo 1 was 2.86 x 108 N, what was the surface area of the satellite? Given
that the surface area of a sphere is 4πr2, what was the radius of the satellite?
8. A ball strikes the pavement with a force of 5.0 N. If the pressure exerted on the
pavement is 9.6 x 103 Pa, what is the area of contact between the ball and the
9. A neutron star is a remnant of a massive star that has undergone an explosion called
supernova. Suppose a neutron star is spherical with a radius of 6.0 km, its surface
consists of closely packed neutrons, and the pressure beneath the surface layer of
neutrons is 1.2 x 1016 Pa. If the surface area of a sphere is 4πr2, what force is exerted by
the neutrons?