# Tutor profile: Shae S.

## Questions

### Subject: Mechanical Engineering

An oil cooler in a high performance engine has an outside surface area 0.12 m2 and a surface temperature of 65 degree Celsius. At any intermediate time air moves over the surface of the cooler at a temperature of 30 degree Celsius and gives rise to a surface coefficient equal to 45.4 W/ m 2 K. Find out the heat transfer rate.

Q = (T2 – T1) A h = 0.12 (65-30) 45.4 = 190.68 W.

### Subject: Calculus

Question 2 True or False. If F(x) = ∫ -23x sin(t) dt then the second fundamental theorem of calculus can be used to evaluate F '(x) as follows F '(x) = sin (3x)

False. Note that the upper limit in the integral above is 3x and not x, hence the integral above has the form F(x) = ∫ -2u(x) f(t) dt Using the chain rule, we can write F '(x) = dF / du * du / dx = 3 sin (3x)

### Subject: Materials Science

In terms of steel vs. aluminum, which of these metals displays an infinite life section on an SN curve? Why does this metal behave this way in comparison to the other?

Steel is the metal that displays an infinite life section on its SN curve. SN curves are a fatigue depiction as they plot stress vs. the number of cycles a material undergoes in cyclic loading. Steel at a specific low stress value will not fail as dislocation motion is inhibited by the number of dislocations that have occurred within the material. This disallows cracks within the material from propagating further leading to fatigue failure. Aluminum on the other hand does not have internal properties which inhibit cracks from propagating further at low stress levels, and thus aluminum even at minimal stress levels will eventually fail under cyclic loading.

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