A block is released from rest at the top of a rough ramp. There is significant friction between the block and the ramp, but the block's speed increases as the block slides down the ramp. Which of the following correctly indicates whether the total mechanical energy of the block-Earth system decreases or remains the same, and provides a valid justification? (A) Decreases, because a force external to the system is dissipating energy (B) Decreases, because the gravitational potential energy of the system decreases (D) Stays the same because gravitational potential energy is converted into kinetic energy because energy is always conserved (D)

The total mechanical energy of the block-Earth system decreases because there is friction between the block and the ramp. Friction is a non-conservative force that dissipates mechanical energy as thermal energy, which means some of the gravitational potential energy is transformed into heat rather than being entirely converted into kinetic energy. This energy loss due to friction leads to a decrease in total mechanical energy. Furthermore, while the gravitational potential energy decreases as the block descends, not all of that potential energy is converted into kinetic energy due to frictional losses. This friction converts some energy into heat, which isn't part of the mechanical energy of the system, confirming that the total mechanical energy indeed decreases as the block slides down the ramp.