1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: In need some help with this problem

  1. Jan 25, 2017 #1
    (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

    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?
  2. jcsd
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted