The discussion revolves around calculating the calories generated in the brakes of a car with a mass of 1000 kg traveling at a speed of 3 m/sec until it comes to a full stop. The participants are examining the kinetic energy involved and its conversion to kilocalories.
There is an ongoing exploration of the calculations and interpretations of results. Some participants express uncertainty about the reasonableness of the calculated energy in kilocalories, while others question the assumptions regarding the conversion factors and the context of the problem.
Participants highlight potential confusion regarding the distinction between gram calories and kilocalories, as well as regional differences in numerical notation. There is also a mention of the expected energy required to boil water, which adds to the discussion about the validity of the calculated values.
I get your answer. Is there perhaps a confusion between decimal comma and decimal point?Karol said:Homework Statement
A 1000 kg mass car is driving at 3 [m/sec], how many kcal develop in the brakes till full stop
Homework Equations
Kinetic energy: E=\frac{1}{2}mv^2
Energetic equivalent of a kcal: 4186 [joule]
The Attempt at a Solution
##E=\frac{1}{2}1000\cdot 9=4500[joule]##
##\frac{4500}{4186}=1.07[kcal]##
It should be 1000 times bigger, 1,075[kcal]
I mean I agree with your answer, a bit over one kcal. But in continental Europe, that could be written 1,075, no?Karol said:by you get my answer you mean you also get the same result? i don't know if there's a confusion between a comma and a decimal point, but please tell me if the result of 1 kcal is reasonable? it isn't, right? so my answer isn't correct
Bear in mind that I do not know where you are or where your textbooks come from. Many on these forums are in continental Europe. I'm trying to understand why you are told the right answer is "1,075 kcal", when you and I both calculate it as just over 1 kcal.Karol said:I don't know about europe, I'm interested in my result.
No, 1 kcal seems reasonable to me. 3m/s is not very fast. I would not expect the generated heat to be enough to boil off a litre of water![/QUOTE]1.07 kcal seems to me too low for that mass and speed, isn't it? and 1075 cal are gram calories, the heat needed to raise the temperature of one gram of water. my result is indeed 1075 gram calories, but i ask about kg calories, kcal. i think the answer must be 1075 kcal, it seems more reasonable