A box of weight $30\,\text{N}$ is released from rest on a ramp inclined at an angle of $30^\circ$ to the horizontal. As the box moves down the ramp, it descends a vertical distance of $8.0\,\text{m}$. While it is moving, a constant frictional force of $10\,\text{N}$ acts on the box. What is the kinetic energy of the box after it has fallen through this distance?
- A$80\,\text{J}$
- B$160\,\text{J}$
- C$240\,\text{J}$
- D$400\,\text{J}$