A wooden block is placed on the rough top surface of a board. The board is then lifted at one end until the block slides down it with constant velocity $v$. What describes the forces acting on the block while it is sliding at constant velocity?
- AFrictional force on block: down the board; resultant force on block: down the board
- BFrictional force on block: down the board; resultant force on block: zero
- CFrictional force on block: up the board; resultant force on block: down the board
- DFrictional force on block: up the board; resultant force on block: zero