 The velocities "V"A and "V"B of the points "A" and "B" are related by the constant length of the rope, that is
or
The negative sign shows that the velocity of the load is opposite to the velocity of the applied force, which means as we pull down on the rope the load moves up.Let "V"A be positive downwards and "V"B be positive upwards, so this relationship can be written as the speed ratio
where 2 is the number of rope sections supporting the moving block.Let "F"A be the input force applied at "A" the end of the rope, and let "F"B be the force at "B" on the moving block.