You are served a hot cup of coffee and room-temperature cream at a restaurant. You want to wait a few minutes before you drink the coffee, and you want it to be as hot as possible when you drink it. Should you pour the cream in the coffee:
b) Just before you drink it
c) It doesn't matter
"Temperature difference" is the driving force for the heat transfer.
Since the coffee is initially very hot and hence it will be cool down at a very fast rate.
If we add cream immediately : The temperature will initially go down for sure but then will cool down at the slower rate as coffees mixed with cream is cooler than coffee alone and therefore heat cool down rate is less. Also, the cream will increase the mass of the content in the cup and hence larger mass will take more time to cool down.
Hence cream should be added immediately
You are strolling in the woods where you find a man lying dead. Next to him, you find a piece of rock. You do not find any other weapon alongside. There is no one around and the dead person is wearing clothes with red, blue and yellow color.
Can you guess who the person is and what killed him?