g
g(R+5 km)2R2\frac{\mathrm{g}(\mathrm{R}+5 \mathrm{~km})^{2}}{\mathrm{R}^{2}}R2g(R+5 km)2
0
gR2(R+5km)2\frac{g R^{2}}{(R+5 k m)^{2}}(R+5km)2gR2