A block of mass M is released from rest at point 1, as shown in the figure. The block slides without frictional forces along the circular arc but encounters frictional forces as soon as it reaches the horizontal portion of the track at point 2. The block travels a distance D along the horizontal track before coming to rest at point 3. Consider the block-Earth system. In terms of the mechanical energy of the system, which of the following claims is correct, and why?
answer choices
The system is closed because a net force is exerted on the block.
The system is open because a net force is exerted on the block.
The system is open because the velocity is zero at points 1 and 3.
The system is closed because the velocity is zero at points 1 and 3.
