Answer to Question #105123 in Classical Mechanics for Franco Yap

Question #105123
1. In the queue at the bus stop, two students (with masses 80 and 60 kg respectively) are standing a distance 0.7 m apart. What is the magnitude of the gravitational force between them?

Treat both objects as point masses, use G = 6.67×10^−11 Nm^2 kg^−2.

F = ___ micro newtons (to one significant figure, and note the units)

2. Ceres is the largest asteroid. Its mean radius is 476 km and its mass is 9.4×10^20 kg. Using this, and G = 6.67×10^−11 Nm^2 kg^−2, and approximating it as a sphere, compute the speed required to escape the gravity on the surface of Ceres.

Speed = ___ m.s^ (to two significant figures, don't use scientific notation)
1
Expert's answer
2020-03-13T10:56:45-0400

1.

Gravitational force is given by Gm1m2r2\dfrac{Gm_1m_2}{r^2}

6.67×1011×80×600.72\dfrac{6.67\times10^{-11}\times80\times60}{0.7^2}

65338.8×10116.5×107N65338.8\times10^{-11}\\6.5\times10^{-7} N


2.

Escape velocity is given by 2GMR\sqrt{\dfrac{2GM}{R}} =2×6.67×1011×9.4×1020476×103=0.26×106m/s=\sqrt{\dfrac{2 \times 6.67\times10^{-11}\times9.4×10^{20}}{476\times10^3}}=\sqrt{0.26\times10^6}m/s

=0.5×103m/s=0.5\times10^3 m/s



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