Observation

 

This is a question on orthographic projection.  A block is given inclined at 300 to the horizontal and candidates were to draw the plan and end elevation.  Candidates were expected to properly position the rectangular block on the front elevation and then draw the plan with the correct given breadth.

Most of the candidates placed the block flat, they could not draw the rectangular block as given and almost all failed to draw the plan with the required breadth.

            Candidates were expected to:

A.        THE GIVEN VIEW

(i)         draw MN at 30o to the horizontal;                                         
(ii)        draw the rectangle;                                                    
(iii)       use correct scale.       

B.           THE PLAN

(i)         project from the front elevation to plan;                                
(ii)        draw the breadth of the block on plan; 

(iii)draw 4 vertical lines (3 outlines, 1 hidden);               

(iv)draw 2 horizontal lines.

                                                           
C.        END VIEW

(i)project from front elevation and plan;

(ii)draw 4 horizontal lines (3 outlines, 1 hidden);

(iii)draw 2 vertical lines;

(iv)draw neatly.

The solution is shown below:

RECTANGULAR BLOCK

 

           
(b)        Figure 2 shows a polygon: sides PQ = QR = 40; PT = RS = 60 and ST = 80.

(i)Draw the given polygon.

(ii)Draw a triangle equal in area to the polygon

(iii)Measure and state all the sides of the triangle.

This is a question on figure of equal areas.  A given pentagon is to be reduced to a triangle of equal area to the polygon.  Candidates were expected to join points P and Q to S and parallel lines are drawn respectively to PS and QS to locate the points on the base of the triangle.  Many of the candidates who attempted this question were able to construct the triangle but failed to state the sides of the triangle.  Also, many of the candidates failed to draw the parallel lines.

Candidates were expected to do the following:

 

DRAWING THE POLYGON

(i)draw the base PQ;                                                                        

(ii)draw lines QR at 30oand PT at 60oto the horizontal;       

(iii)locate point S and complete the pentagon PQRST;        

(iv)use the correct scale.

                                                     

 CONVERTING TO TRIANGLE

(i)extend line PQ on both ends;                                          

(ii)join points P to S and draw a line  from point T parallel to PS to locate

 point U;               

(iii)join point Q to S and draw a line from R parallel to QS to point   locate point V;                                                     

(iv)draw lines US and VS to complete the triangle UVS.    

 

 STATING THE LENGTHS OF THE TRIANGLE

State the lengths as follows:
lengths UV = 138 + 1, VS = 78 + 1 and US = 132 + 1        

The solution is shown below:

 

CONVERSION OF IRREGULAR POLYGON