
(a)
The escape velocity for the moon.
(a)

Answer to Problem 63P
The escape velocity of Moon is 2.38 km/s.
Explanation of Solution
Formula Used:
The escape velocity of a particle to escape the gravitational field of the Moon is given as
v=√2GMR
Where, G is the gravitational constant of Moon is 6.67×10−11 N⋅m2⋅kg−2 , 1737.1 km is the radius of Moon, mass of Moon is 7.342×1022kg
Calculation:
Substitute the values:
v=√2GMR=√2×6.67×10−11×7.342×10221737.1×103=2.38 km/s
Conclusion:
The escape velocity of Moon is 2.38 km/s.
(b)
The velocity of the particle in the earth’s environment.
(b)

Answer to Problem 63P
The velocity withwhich particle will enter the Earth’s surface is 1.85×106m/sec
Explanation of Solution
Given Data:
The energy conservation is given as
Initial Total Energy==Final Total EnergyP.Ei+K.Ei=P.Ef+K.Ef (1)
Particle at moon starts with a K.Ei with an escape velocity vm=√2GMmRm ,where G is the gravitational constant whose value is 6.67×10−11 Nm2kg-2 , Mm is the mass of the moon and Rm is the radius of the moon, vm is the escape velocity from the moon which is the initial velocity of the particle.When particle is at the surface of moon, then the potential energy of particle and Earth is neglected as it is far from the Earth. Therefore, P.Ei=0 . As the particles reaches the Earth’s surface, the particle and earth potential energy is final and given as P.Ef=−GMEmpRE , ME and RE is the mass and radius of the Earth respectively and mp is the mass of the particle.
Formula Used:
Using equation 1, write
K.Ei=P.Ef+K.Ef12mpvi2=−GMEmpRE+12mpvf2
Putting the initial velocity equal to the escape velocity from moon, we can write:
12mp(√2GMmRm)2=−GMEmpRE+12mpvf2
12mp2GMmRm=−GMEmpRE+12mpvf2
Solving for final velocity vf
vf=√G(MmRm+MERE)
Calculation:
vf=√6.67×10−11(7.342×10221737.1×103+5.972×10226371×103)
vf=1.85×103m/s
Conclusion:
The velocity withwhich particle will enter the Earth’s surface is 1.85×103m/s
(c)
The ratio of final to initial kinetic energy of the particle.
(c)

Answer to Problem 63P
The ratio of final to initial kinetic energy of the particle is 24.86.
Explanation of Solution
Given data:
Particle at moon starts with a K.Ei with a escape velocity vm=√2GMmRm ,where G is thegravitational constant whose value is 6.67×10−11 Nm2kg-2 . Mm is the mass of the moon and Rm radius of the moon, vm is the escape velocity from the moon which is the initial velocity of the particle.
Formula Used:
When particle is at the surface of moon, then the potential energy of particle and Earth is neglected as it is far from the Earth. The velocity with which particle will enter the Earth’s surface is vf=√G(MmRm+MERE)
Ratio is given as below:
K.EfK.Ei=12mpvf212mpvi2=vf2vi2
K.EfK.Ei=vf2vi2=G(MmRm+MERE)2GMmRmK.EfK.Ei=(MmRm+MERE)×Rm2Mm
K.EfK.Ei=(1+MERERmMm)×12
Calculation:
Putting the values of radius and mass of earth and moon, we get,
K.EfK.Ei=(1+(5.972×10246371×17373.342×1022))×12K.EfK.Ei=24.86
Conclusion:
The ratio of final to initial kinetic energy of the particle is 24.86 .
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Chapter 7 Solutions
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