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Concept explainers
(a)
Moon’s gravitational field at the side of Earth which is facing Moon.
(a)
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Answer to Problem 55PQ
Moon’s gravitational field at the side of Earth facing Moon is 3.44×10−5 m/s_.
Explanation of Solution
Write the equation to find the gravitational field due to Moon at a distance of Moon-Earth distance minus radius of Earth.
g=GMmoonr2 (I)
Here, g is the gravitational field, G is the gravitational constant, Mmoon is the mass of Moon, d is the Earth-Moon distance, Re is the radius of Earth.
Write the expression to find r.
r=d−Re
Here, d is the Earth-Moon distance, and Re is the radius of Earth.
Use the expression for r in equation (I).
g=GMmoon(d−Re)2 (II)
Conclusion
Substitute 6.67×10−11 Nm2/kg2 for G ,7.35×1022 kg for Mmoon,3.84×108 m for d, and 6.37×106 m for Re in equation (II) to get g
g=(6.67×10−11 Nm2/kg2)(7.35×1022 kg)(3.84×108 m−6.37×106 m)2=3.44×10−5 m/s2
Therefore, Moon’s gravitational field at the side of Earth facing Moon is 3.44×10−5 m/s_.
(b)
Moon’s gravitational field at the side of Earth facing away from Moon.
(b)
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Answer to Problem 55PQ
Moon’s gravitational field at the side of Earth facing away from Moon is 3.22×10−5 m/s_.
Explanation of Solution
Write the equation to find the gravitational field due to Moon at a distance of Moon-Earth distance plus radius of Earth.
g=GMmoonr2 (III)
Write the expression for r.
r=d+Re
Substitute the expression for r in equation (III).
g=GMmoon(d+Re)2 (IV)
Conclusion:
Substitute 6.67×10−11 Nm2/kg2 for G, 7.35×1022 kg for Mmoon, 3.84×108 m for d, and 6.37×106 m for Re in equation (IV) to get g.
g=(6.67×10−11 Nm2/kg2)(7.35×1022 kg)(3.84×108 m+6.37×106 m)2=3.22×10−5 m/s2
Therefore, Moon’s gravitational field at the side of Earth facing away Moon is 3.22×10−5 m/s_.
(c)
The gravitational field of Moon at the center of Earth.
(c)
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Answer to Problem 55PQ
Moon’s gravitational field at the center of Earth is 3.32×10−5 m/s_2.
Explanation of Solution
Write the equation to find the gravitational field due to Moon.
g=GMmoond2 (IV)
Conclusion:
Substitute 6.67×10−11 Nm2/kg2 for G, 7.35×1022 kg for Mmoon,and 3.84×108 m for d in equation (IV) to get g
g=(6.67×10−11 Nm2/kg2)(7.35×1022 kg)(3.84×108 m)2=3.32×10−5 m/s2
Therefore, Moon’s gravitational field at center of Earth is 3.32×10−5 m/s_.
(d)
Sketch Earth and include the three vectors from parts (a) through (c).
(d)
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Answer to Problem 55PQ
Sketch of Earth and the three vectors from parts (a) through (c) is shown in Figure 1.
Explanation of Solution
Figure 1 shows the sketch of the Earth and the magnitude and direction of the gravitational field vectors found in part (a), (b) and (c).
Conclusion:
Therefore, Sketch of Earth and the three vectors from parts a through c is shown in Figure 1.
(e)
The reason why there are two tides a day on most places on Earth due to Moon.
(e)
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Answer to Problem 55PQ
There are two tides a day on most places on Earth due to Moon because the force is larger on bodies of water closer to Moon and smaller on bodies of water on far side of Earth.
Explanation of Solution
Figure below shows the Earth and Moon. High tides and low tides on either side of Earth are due to the lunar activity on Earth. The gravitational pull by Moon on Earth causes high tide and low tide.
The force of Moon is large at water bodies which are close to Moon and lowest on water bodies which are far away. Thus the amplitude or strength of tides is dependent on the distance of the water body and Moon. This is the reason for two types of tides on Earth.
Conclusion:
Therefore, there are two tides a day on most places on Earth due to Moon because the force is larger on bodies of water closer to Moon and smaller on bodies of water on far side of Earth.
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Chapter 7 Solutions
Physics For Scientists And Engineers: Foundations And Connections, Extended Version With Modern Physics
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