WAEC Physics 2014 Paper

Concept:Velocity ratio of a screw-jack is the ratio of the distance moved by the effort to the distance moved by the load in one complete revolution.Explanation:In one full turn of the tommy bar, the effort moves along the circumference of a circle of radius $r$.So, distance moved by effort $= 2\pi r$.During the same one turn, the screw advances by one thread separation, which is the pitch $P$.So, distance moved by load $= P$.Therefore, velocity ratio is given by:$$\text{V.R.} = \frac{\text{distance moved by effort}}{\text{distance moved by load}} = \frac{2\pi r}{P}$$Answer:$$\frac{2\pi r}{P}$$This matches option B.