4. (a) Explain why the efficiency of a machine cannot be 100%. (b) A screw jack, 25% efficient and having a screw of pitch 0.4cm is used to raise a load through a certain height. If in the process the handle turns through a circle of radius 40cm, calculate the Velocity ratio of the machine (i) The mechanical advantage of the machine (in)Effort required to raise a load of 100N with the machine [π=3.14]​