A block of mass m m\,m is sliding down a rough ramp inclined at an angle θ \theta\,θ to the horizontal at a constant velocity vvv, as shown in the diagram.
Which statement correctly describes the forces acting on the block?
The resultant force on the block is non-zero and points down the incline because the block is moving down the slope.
The magnitude of the frictional force fff is equal to WsinθW \sin\thetaWsinθ because the net force acting on the block is zero.
The normal reaction force RRR is equal in magnitude to the weight WWW because the block is in equilibrium perpendicular to the incline.
The magnitude of the frictional force fff is greater than WsinθW \sin\thetaWsinθ to prevent the block from accelerating.