Q&A - P4 Science

[dazzlego]

Jamesbond:

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what could be the answer for this?...Help needed...Thx.

The answer is (3) W and X only. W can be obtained placing the whole mixture of the 4 substances together in water. Then, use a magnet on the remaining mixture (X,Y,Z), and a mixture of Y and Z will be taken out. What is left is X. Tada!

[Jamesbond]

dazzlego:

Jamesbond:

http://i46.tinypic.com/slpws9.jpg\">

what could be the answer for this?...Help needed...Thx.

The answer is (3) W and X only. W can be obtained placing the whole mixture of the 4 substances together in water. Then, use a magnet on the remaining mixture (X,Y,Z), and a mixture of Y and Z will be taken out. What is left is X. Tada!

Thank you Dazzlego....

[milomilo]

Help needed:


Gopal pumped air into 2 footballs. The footballs when fully inflated each have a capacity of 400cm3. For football A, he pumped 350cm3 into it and for football B he pumped 405cm3. Which of statement is correct?

(1) Ball A is heavier than Ball B
(2) Ball B has 405cm3 of air inside it
(3) Both Ball A and B has 400cm3 of air inside it
(4) Ball A and Ball B are of the same mass after air was pumped in.

Note: Answer (1) and (4) are obvious wrong.

Thanks!

[Nebbermind]

milomilo:

Help needed:


Gopal pumped air into 2 footballs. The footballs when fully inflated each have a capacity of 400cm3. For football A, he pumped 350cm3 into it and for football B he pumped 405cm3. Which of statement is correct?

(1) Ball A is heavier than Ball B
(2) Ball B has 405cm3 of air inside it
(3) Both Ball A and B has 400cm3 of air inside it
(4) Ball A and Ball B are of the same mass after air was pumped in.

Note: Answer (1) and (4) are obvious wrong.

Thanks!

(2) Air can be compressed so vol should be 400cm3
(3) Since A is not fully inflated, it cannot be 400cm3

Is this question from assessment bk or school's exams?

[milomilo]

In one of the school exam papers. Model answer is (3).


Also think cannot be 400cm3 because not fully inflated. But then what will be the next best answer??

[Nebbermind]

milomilo:

In one of the school exam papers. Model answer is (3).


Also think cannot be 400cm3 because not fully inflated. But then what will be the next best answer??

I supposed no correct answer.

[verykiasumummy]

milomilo:

Help needed:


Gopal pumped air into 2 footballs. The footballs when fully inflated each have a capacity of 400cm3. For football A, he pumped 350cm3 into it and for football B he pumped 405cm3. Which of statement is correct?

(1) Ball A is heavier than Ball B
(2) Ball B has 405cm3 of air inside it
(3) Both Ball A and B has 400cm3 of air inside it
(4) Ball A and Ball B are of the same mass after air was pumped in.

Note: Answer (1) and (4) are obvious wrong.

Thanks!

hi offering my ans :

option 2 is wrong because although 405cm3 of air is pumped inside, the capacity of the ball is only 400cm3 so air will be compressed to fit into the same ball capacity of 400cm3 only.

option 3 is the correct answer. although only 350cm3 is pumped into ball b, air can space itself out to occupy the same capacity of the ball so ball b will also have 400cm3 of air.

take note of the concept : air can be compressed to occupy a smaller space; air can also be spaced out to occupy a bigger space because air has no definite volume.

hope this clarifies.

[Nebbermind]

hi vksmummy


If the ball has a regular shape, I would agree with you.
But if u r familiar with football, when it has less than the required vol of air, ie, 400cm3, it will not be ‘perfectly’ round. Therefore, the volume cannot be 400cm3.

[Bookwrappers]

Hello nebbermind, the ans from vksm is correct. I know what u mean too. No matter whether the ball is round or not, the volume of air is the same. This is the unique proerty of air.

[jedamum]

tianzhu:

teh_oh:

My child got the Q23 of the same paper incorrect. Do you mind explaining how you/your child get your/her answer, as I am not good at the topic of matter.

Hi

Good Morning.

I think students learned that a gas has no definite volume and that it can be compressed in PSLE science.

Going back to your question, I think the answer lies in the state of the basketball before air is pumped in.

1)If it is in the deflated state, as you pump in more air, the shape of the basketball changes, hence volume increases.

2)If the basketball is already pumped to its recommended pressure, then pumping in more air may not increase its volume. The shape of the ball does not change. You can imagine the ball as similar to a container of fixed volume.

Best wishes

so Nebbermind same view as Tianzhu? :?
if yes..it is 2 against 2 already.
for me, i dunno. keen to find out. thanks!