An astronaut question?

Question

An astronaut on another planet drops a 1 kg rock from rest. The astronaut notices that the rock falls 2 meters straight down in one second. On this planet, how much does the rock weigh?

The answer given is 4N.

I don't understand. Its weigh is the gravity on earth, so it would be 9.8N. Why is it 4N?

Answer 1

Gravity is directly proportional to mass. If the answer is 4N, then the mass of the planet on which the rock was dropped must be approx. 0.41 that of the earth:

4 / 9.8 = 0.408

If the rock weighs 1 kg on the other planet, then it must weigh 2.45 kg on earth:

(9.8 / 4) * 1 kg = 2.45 kg