Answer:
5.4 g
Explanation:
The stone is already in motion, so the only energy it has is kinetic. The formula for kinetic energy is:
[tex]KE=\frac{1}{2} mv^{2}[/tex]
You can substitute the 390 J in for KE and 12 m/s in for v. After that, the equation looks like:
[tex]390=\frac{1}{2} m12^{2}[/tex]
Then do basic algebra and m=5.4 g
