Question Bank

Unit 2

1. What is loci of points?

Ans –

Loci of points:

A locus (plural loci) is the path of a point which moves in space.

(i) The locus of a point P moving in a plane about another point O in such a way

That its distance from it is constant, is a circle of radius equal to OP (fig. 1).

Figure 1

(ii) The locus of a point P moving in a plane in such a way that its distance from afixed line AB is constant, is a line through P, parallel to the fixed line(fig. 2).

Figure 2

(iii) When the fixed line is an arc of a circle, the locus will Abe another arc drawn through P with the same centre·(fig. 3).

Figure 3

(iv) The locus of a point equidistant from twofixed points A and B in the same plane, isthe perpendicular bisector of the line joiningthe two points (fig. 4).

Figure 4

(v) The locus of a point equidistant from twofixed non-parallel straight lines AB and CDwill be a straight line bisecting the anglebetween them (fig. 5).

Figure 5

In simple mechanisms, it is often necessary to know the paths of points on their moving parts. These are determined by assuming a number of different positions of the moving parts and then locating the corresponding positions of the points.

2. What is slider crank mechanism?

Ans –

The slider crank mechanism shown diagrammatically in fig. 6 is one of the

Simplest mechanisms and it is used in internal combustion engine, sewing machineand printing press etc. The end A of the connecting rod AB is connected to thecrank OA which rotates about 0. The other end B is attached to a slider whichslides along a straight line. The locus of A will be a circle and that of the end Bwill be a straight line. The locus of any other point, say P, on the connecting rodwill be neither a circle nor a straight line and may be determined:

(i) by assuming various positions of the crank-end A,

(ii) by obtaining the corresponding positions of the end B and finally

(iii) by locating the positions of P on the lines joining the first two positions.

A smooth curve drawn through the points thus located will be the locus of P.

Such curves are known as coupler curves.

3. What is four bar mechanism?

Ans –

This mechanism consists of four links. It is widely used in locomotive, steeringmechanism of the car, pantograph and straight-line mechanisms.