Question

The escape speed for a planet of mass M and radius R is 16.3 kms^-1.

Calculate the escape velocity from a planet of mass four times the mass and twice the radius.

Answer 1

$$v=\sqrt{\frac{2GM}{r}}\\v'=\sqrt{\frac{2G(4)M}{2r}}=\sqrt{2}v\\v'=\sqrt{2}16.3=23.1\frac{km}{s}$$