# In need some help with this problem

Tags:
1. Jan 25, 2017

### XFACTORMAN

(mentor note: moved from general physics to here hence no template)

Hi, the teacher gave me this problem to solve. So i hope you can help me with it. Here is the problem:
John poured 150ml ob boiling water in 2 cups made out of polystyrene. Cups are open on the top so heat goes out there. Temperature of the outside air is 20°C. In 1 cup he add 5 mm thick layer of hot oil. He measured starting temperatures and then he measured temperatures again after 10 min. He measured the mass of water and water+oil before and after 10 min. Here are the resaults:
-cup 1 (only water)
starting temp.: 96°C
finnish temp.: 64°C
starting mass: 149.4g
finnish mass: 142.42g

-cup 2(with oil on top)
starting temp.: 96°C
finnish temp.:91°C
starting mass: 164.72g
finnish mass: 164.70g
The surface of the both cups is 0.003 m2

Questions:
1.Why did the water covered with oil cooled down slower that the one with no oil? Show with calculations.
2.Why did John use oil with temperature around 100°C and not oil with room temperature? How would the resaults change if he used room temeprature oil?
3. Which other physical values, which are relevant, can you calculate from this informations?