According to Copernicus, retrograde motion for Venus must occur around : a. greatest elongation, when the planet is farthest from the Sun.
b. inferior conjunction, when it passes between us and the Sun.
c. superior conjunction, when the planet is on the far side of the Sun.
d. opposition, when the planet lies opposite the Sun in the sky.
e. quadrature, when the planet is 90 degrees away from the Sun.

Asteel tube (k=50 w/mk) of inner and outer diameter di = 20mm and do=26mm, respectively, is used to transfer heat from hot gases flowing over the tube (h-hot = 200w/m2k) to cold water flowing through the tube (h-cold = 8000 w/m2k). what is the cold-side overall heat transfer coefficient uc? to enhance heat transfer 16 straight fins of rectangular profile are installed longitudinally along the outer surface of the tube. the fins are equally spaced around the circumference of the tube, each having a thickness of 2mm and a length of 15mm. what is the corresponding overall heat transfer coefficient uc? *solve for uc in both cases*