Q&A - P3 Science

[iFruit]

match3frog:

P4 Question:


A picture showing 3 plastic bags tied at the top. Bag A is the smallest in size, Bag B is bigger than Bag A and Bag C is the biggest.

Q: Air is trapped inside the 3 plastic bags, A B and C.

Which of the following about the bags of air is definitely true?
1) The air in C is the most compressed
2) The air in the three bags has definite shape
3) The mass of air in B is bigger than that in A and smaller than that in C
4) The volume of air in B is bigger than that in A and smaller than that in C.

Answer is 4.
Can I know why the 3rd answer if not true? Won't a bigger bag contain more air and therefore has a bigger mass than a smaller one?

Thanks!

Air in Bag A could be compressed and could have more mass than Bag B. All we can be certain about are the volumes of the air in the three bags.

HTH

[match3frog]

Thank you iFruit! That makes sense!

[elkniwt]

Dear atutor2001, peggy and the kiasu student,


Thank you very much for your responses and help.

:thankyou:

[elkniwt]

Dear match3frog,


This is what I think. As air can be compressed, if two bags of the same volume, one contains compressed air and the other non-compressed air, the mass of the compressed air will be more. Hence if a bigger bag containing non-compressed air may not have a bigger mass than a smaller bag containing compressed air.

Regards.

match3frog:

Answer is 4.
Can I know why the 3rd answer if not true? Won't a bigger bag contain more air and therefore has a bigger mass than a smaller one?

Thanks!

[tianzhu]

Hi match3frog


Your question may be from Toanan Science SA2 2009.

Please go to page 7 of this link to see Q8.
http://www.orlesson.org/orp/09Sc/P4-09-Sc-SA2-TaoNan.pdf

This question asks for a statement which is definitely true.
To be definite means free of all ambiguity, uncertainty. With this in mind, let's begin our journey to sieve out the correct answer.

In primary science students learned that air has no definite shape and volume. I also has weight/mass.

(1)From the picture, we are unable to tell if the air in C is the most compressed. It may or may not be. There is insufficient information for us to draw a definite conclusion.

(2)We can see that the three bags are of different shapes.

(3)By looking three plastic bags, we are unable to confirm if this statement is true. Again it may or may not be. There is insufficient information for us to draw a definite conclusion.

(4)This statement is definitely true.

Therefore, the answer is option (4)

Best wishes

[tianzhu]

JayneLL:

could you let me know where you get these questions.

Hi

This question may be from Toanan Science SA2 2009.

Please go to page 7 of this link to see Q8.
http://www.orlesson.org/orp/09Sc/P4-09-Sc-SA2-TaoNan.pdf

Best wishes

[atutor2001]

match3frog:

A picture showing 3 plastic bags tied at the top. Bag A is the smallest in size, Bag B is bigger than Bag A and Bag C is the biggest.

3) The mass of air in B is bigger than that in A and smaller than that in C

Can I know why the 3rd answer if not true? Won't a bigger bag contain more air and therefore has a bigger mass than a smaller one?

Thanks!

Hi match3frog

I always visualise air as tiny little dots (molecules) floating about. Its volume depends on the space given for these dots to wander about. The volume of \"1 dot of air\" place in a 10 cu cm tube is considered to have a volume of 10 cu cm. \"1000 dots of air\" in a 5 cu cm tube is considered to have a volume of 5 cu cm. But the mass of 1000 dots of air is definitely more than 1 dot of air although its volume is smaller (as it is placed in a smaller tube). Therefore, we cannot judge whether which bag of air is heavier by looking at the volume alone.

[match3frog]

Dear elkniwt, tianzhu & atutor2001,


Thank you all for the clear and concise explanations!

[peggy]

Can anyone help with this P4 qtn ?


John was running around the field during recess before his teacher brought the class into an air-conditioned room. He felt cold after he entered the room.

A) Explain why John felt cold in the air conditioned room.
B) There are air spaces in a woollen jacket.
When John put on his jacket, he felt warm. Explain how the jacket had kept John warm.


Many thanks in advance !

[iFruit]

peggy:

Can anyone help with this P4 qtn ?


John was running around the field during recess before his teacher brought the class into an air-conditioned room. He felt cold after he entered the room.

A) Explain why John felt cold in the air conditioned room.
B) There are air spaces in a woollen jacket.
When John put on his jacket, he felt warm. Explain how the jacket had kept John warm.


Many thanks in advance !

1) Heat transfers/travels from Johns body to the surrounding cold air and hence he feels cold.

2) Wool is a poor conductor of heat so the air spaces in the jacket retain the heat keeping John warm.

HTH