7. what is the kinetic energy of a 3 - kilogram ball that is rolling at 2 meters per second?

Explanation:

Step1: Recall kinetic - energy formula

The formula for kinetic energy is $K = \frac{1}{2}mv^{2}$, where $m$ is the mass and $v$ is the velocity.

Step2: Substitute given values

Given $m = 3\ kg$ and $v = 2\ m/s$. Substitute into the formula: $K=\frac{1}{2}\times3\times(2)^{2}$.

Step3: Calculate the result

First, calculate $(2)^{2}=4$. Then, $\frac{1}{2}\times3\times4 = 6\ J$.

Answer:

$6\ J$