Question

If mass of a planet is 8 times that of the earth and its radius is twice the radius of

the earth, what will be the escape velocity of that planet? (Escape velocity for the

earth – 11.2 km/s )

Answer 1

The equation for finding out escape velocity is v = √(2gr)

Or v = √(2GM/r)

so if the mass increases 8 times, the escape velocity would increase 2 √2 times. And if the radius expands two times, then the escape velocity would reduce by 1/√2. So the net change in escape velocity would be increased :

2 √2 × 1/√2 = 2 times its present value.

Ans: The escape velocity would be 2 times the escape velocity on Earth, that is, 2×11.2 km / s = 22.4 km/s .