Answer:
17.8 kg
Step-by-step explanation:
The force with which the rock hits the ground is the force of gravity, which is also known as weight of the object, and whose magnitude is given by:
![W=mg](https://img.qammunity.org/2020/formulas/physics/middle-school/oq8az7xjzl9h2d74orlcj0v1zet7mbhsgr.png)
where
m is the mass of the object
g is the acceleration of gravity
In this problem, we know the weight of the rock
W = 174 N
We also know the acceleration of gravity,
![g=9.8 m/s^2](https://img.qammunity.org/2020/formulas/physics/high-school/pzbgdnh5dnauj7cfcpu92d9km30p4mlye9.png)
So, we can find the mass of the rock:
![m=(W)/(g)=(174)/(9.8)=17.8 kg](https://img.qammunity.org/2020/formulas/physics/middle-school/34yfpifwy0e291myu4ar40rw0dqb7uxqoj.png)