Question

A rock hits the ground with a speed of 7 m/s and a kinetic energy of 100 J. What is the rock's mass?

Answer 1

mass = (2*KE) / v²
∴ the answer is 200/49 

Answer 2

KE=1/2 times mass times velocity squared. So in this situation your equation would look like this 100J=1/2 times mass times 7 m/s^2. Your answer would be 4.0812 kg