Answer:
<h2>20 kg</h2>
Explanation:
The mass of the rock can be found by using the formula

f is the force
a is the acceleration
From the question we have

We have the final answer as
<h3>20 kg</h3>
Hope this helps you
When mass is doubled, KE is doubled.
When speed is doubled, KE becomes 4 times as great.
When both are doubled (last choice), KE is multiplied by 8 .
To change from mass to weight is Fw = 30 kg * 9.8 m/s^2 = 294 N. To change from weight to mass divide by gravity (9.8 m/s^2).