A wooden block is placed on a rough board. The far end of the board is then lifted until the block moves down the surface of the board with constant velocity $v$. Which row shows the forces acting on the block while it is sliding at constant velocity?
- Africtional force on block: down the plane; resultant force on block: down the plane
- Bfrictional force on block: down the plane; resultant force on block: zero
- Cfrictional force on block: up the plane; resultant force on block: down the plane
- Dfrictional force on block: up the plane; resultant force on block: zero