Now, the answers.
*** 1 ***
You have a new-fangled pistol-grip hand-held laser-beam-aimed InfraRed (IR) temperature sensor.
Your refrigerator went kaplooey. Down the street is the budget used/refurb refrigerator store. They have 3 equal-sized and equal-priced refrigerators on display, plugged-in and running for customers to evaluate, ready to go. You want the best refrigerator for your money and decide to be scientific about this. So, you shoot your IR gun at the middle of each refrigerator's door. You also note that the store's room temperature is 75°F.
Refrigerator #1's door shows 70°F
Refrigerator #2's door shows 65°F
Refrigerator #3's door shows 60°F
Which refrigerator do you buy?
The correct answer is: "I dunno".
Since all 3 are colder than ambient, you can assume that all 3 are cooling. But, without knowing the actual temperature inside the refrigerators, you only have a piece of the puzzle, since you don't know the cold leakage (insulation value) of each refrigerator's door.
#3 could be the coldest, or
#1 could be the coldest, with the best door insulation.
#3 could be the warmest, with the worst door insulation.
Or any combination of these.
*** 2 ***
It's a calm/still severely cold evening, -30°F. The weather guys are predicting that it'll get even colder overnight. You're concerned about your 3 elderly neighbors' well-being, but don't want to intrude unless necessary. Using your IR gun, you stroll outside and take readings of their front doors.
Neighbor #1's front door shows -20°F
Neighbor #2's front door shows 0°F
Neighbor #3's front door shows +20°F
Which neighbor are you concerned about?
The correct answer is: "I dunno".
Since all 3 are warmer than ambient, you can assume that all 3 homes have some sort of heating. But, without knowing the actual temperature inside their homes, you only have a piece of the puzzle, since you don't know the heat leakage (insulation value) of each neighbor's door.
#1 could be the coldest, or
#1 could be the warmest, with the best door insulation.
#3 could be the coldest, with the worst door insulation.
Or any combination of these.
*** 3 ***
You want to purchase a passive room heater, like one of those no-moving-parts oil-filled heaters. The heater store has 3 models on display, plugged-in and heating. You whip out your trusty IR gun and take readings of each heater. You also note that the store's room temperature is 75°F.
Heater #1 shows 130°F
Heater #2 shows 125°F
Heater #3 shows 120°F
*** Update ***
*** Heaters #1 & #2 are the size of golf balls, heater #3 is the size of a washing machine. ***
Now, which heater do you buy?
The correct answer is: "I dunno".
Since all 3 are warmer than ambient, you can assume that all 3 heaters have some sort of heating. But, heater #3 has a much larger radiating surface, and will probably put out more total heat.
But it won't fit under your computer desk to warm your feet.
*** 4 ***
You're out ridin' your XS650, with 2 buddies who are also ridin' XS650s. It's a super-hot 106°F summer day, and ya'll are concerned about overheating damage. After a highway-speed ride, everybody comes to a stop, you whip out your IR gun and take quick readings of the cylinders of all 3 bikes.
Your engine shows 290°F
Tom's engine shows 270°F
Harry's engine shows 250°F
Whose bike is in danger of overheat damage?
*** Update ***
*** Harry's engine is painted black ***
Now, whose bike is in danger of overheat damage?
The correct answer is: "I dunno".
Since all 3 are warmer than ambient, you can assume that all 3 bikes have been running. But, without knowing the actual temperatures inside the engines, you only have a piece of the puzzle, since you don't know the total heat dissipation (convective and radiant) of each bike's engine. You also don't know the engine tuning/conditions and demands for highway speeds, which gives insight into the engine's power utilization.
It's logical to assume that all 3 engines are similar, with exposed aluminum cylinder fins, and in that scenario, you'd think that yours is in imminent danger.
However, the engine needs to shed its internal heat. A good heat conduction, poor insulation value, will let that heat escape. As such, that would drive the external temperatures higher. The air-exposed engine with the highest external temperature is radiating the greatest heat, and could be running cooler inside than the others. Then again, it could have a problem and really be hotter than the others.
If you want to reduce the externally measured temperature of your engine, wrap it in a blanket of asbestos. That'll do it, keep all that heat in, the outside will be much cooler. Works great on exhaust pipes, keeps you from roasting your legs. You'll also have a ready supply of molten aluminum. With the exception of properly applied Kal-Gard and certain FAA approved engine paints, expect most engine painting to act as a heat blanket. What does that say about Harry's engine?
A good adjunt to monitoring engine temperatures is an oil dipstick thermometer.
********
This kind of test demonstrates the fascinating 'inductive logic' nature of human thought. When trying to solve a puzzle, in the absence of a complete picture, the human mind will, often unknowingly, 'fill-in' the missing pieces, and lead it down an interesting path.
So, for all of you who read this and thought "I don't know", congratulations. You aced it.