Two objects have masses of 4 MG4MG and 7 MG7MG. How much does the gravitational potential energy between the objects change if the distance between them changes from 320 m320m to 450 m450m?

1 Answer
Mar 15, 2016

Change in gravitational potential energy
=1.69xx10^-6J=1.69×106J rounded to two decimal places

Explanation:

Gravitational potential energy PE_gPEg between two objects of masses m_1 and m_2m1andm2 is given by the relation

PE_g = − (Gm_1m_2)/rPEg=Gm1m2r,
where rr is the separation between their centres and GG is the universal gravitational constant (6.67 xx 10^(−11) m^3 kg^-1 s^-16.67×1011m3kg1s1)

As the distance between their centres changes from r_I=320mrI=320m to r_F=450mrF=450m, the change in gravitational potential energy can be found from
Delta PE_g=− (Gm_1m_2)/r_F-(− (Gm_1m_2)/r_I)
=− (Gm_1m_2)[1/r_F-1/r_I]
Inserting the given values, mass 1Mg=10^3kg
=-(6.67 xx 10^(−11)xx4xx10^3xx7xx10^3)[1/450-1/320]
or =-(186.76 xx 10^(−5))xx(-9.02 dot7xx10^-4)
=1.69xx10^-6J rounded to two decimal places