How much does a 20 kg rock weigh on Earth where g = 9.8 m/s2?

Explanation:

Mass and weight ain't the same thing. So, for calculating weight we would use Newton's 2nd Law of Motion i.e. Force = Mass × Acceleration.

According to question,

The mass is 20kg

Acceleration is 9.8 m/s^2

Putting the given values into the formula,

F = 20 × 9.8

F = 196N

So, the weight of the rock is 196 N

Hope it helps!<3