QUESTION 6 (a) The bar shown in Figure Q2(a) is subjected to tensile load of 150 Kn. If the stress in the middle portions is limited to 160 N/mm², determine the diameter of the middle portion. Find also the length of the middle portion if the total elongation of the bar is to be 0.25 mm. E E = 2.0 + 105N/mm². (12 marks) 150 KN 10 cm DIA 10 cm DIA 150 KN 45 cm Figure Q6(a) (b) A brass bar, having cross-section area of 900 mm², is subjected to axial forces as shown in Figure Q2(b), in which AB = 0.6 m, BC = 0.8 m, and CD = 1.0 m. Find the total elongation of the bar. E = 1.0 + 105N/mm2 . (8 marks) Page 4 of 5 B D 40 KN 70 KN 20 KN 10 KN Figure Q6(b) (TOTAL = 20 MARKS)

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Answer.) Keplerian Telescopes 🔭. :

 The Kepler telescope 🔭 as shown in the figure consists of two converging Lens, one is called Objective lens and another is called eyepiece Lens ....

Now it is given that ;

the object is lying in the front focal plane of the first lens

therefore,

magnification m = -fo/fe = -2

Implies , fo ( objective focal length)

= 2 • fe ( eyepiece focal length) ...

image size = m • object size

image size = -2 •5 mm = -1 cm

for normal adjustment Lenght

L = fo + fe = 3 • fe

for calculation and N.A of the objective lens ;

 hence , the numerical aperture NA = 0.159

answer.....