Q&A - PSLE Science

[Joy]

Hi Tianzhu


Thanks for all the kind words and I really appreciate the piece of advice that you have given...


rgds

tianzhu:

Hi Joy

As parents, we have to know our limitations; there is only so much we can do for our child.

Actually, I am not in favour of a child seeking too much external help unless he/she really needs it. Too much hand holding may not be good in the long run.

We try our best to prepare our kids adequately, but once inside the examination hall, he/she is alone. We cannot replicate the stress that is in major examinations. Factors such as panic, loss of memory creep in. Some kids may be more adaptable to examination conditions than others.

Well, we do our best within our constraints. Beyond that, there is really little else that can be done.No matter how many laps we do in a swimming pool, it will never be enough to prepare us for a swim in the choppy sea.

Hope you’ll enjoy success in your search. But, then PSLE is only two months away.

May your child enjoy success in PSLE.

[tianzhu]

Drdj:

Hi all,

My apologies for uploading so many difficult questions...the past yr school papers do bamboozle me at times !! Hope you can assist me with these queries - I've written down comments in the questions - which says why can't it be answer..etc....thanks in advance

Hi
Hope this helps.

Image 1
Q25 ---- The key point here is weeds are small unwanted plant .Picture those weeds that are growing together with bigger plants .Can they compete with the bigger plants for sunlight? Therefore option (1) is a logical choice.

Q22 --- From Dharma ----- The ball rotates in a clockwise direction towards the boy. Therefore at the point of contact of the ball w/ the ground, the force of motion acts along direction (1). Friction opposes motion, and therefore will act along (3). This is same for wheels of a vehicle moving.

Image 2
Q17 ---The key point here is what you would you infer from the results of the experiment.From background knowledge, we already know that food is a renewable source of energy.

A is obvious; the three foods are sources of energy.
C is logical as dried corn raises the temperature of water to a higher point.
Hence option (2) is correct.

Q18 ---- The size of the food is not within control. For a fair test, we can ensure that the same amount of food ie its mass is constant. Besides this, the intensity of the flame and the amount of water must be consistent.

Image 3
My answer is option (1)
The question states that three rooms A, B and C are of different temperatures, hence (4) is offside.
Option(1) is logical, when warmer water vapours touch a cooler surface, condensation occurs.

Image 4
The darker object sinks in liquid A, but floats in liquid B. The two liquids cannot mix. Play around with the masses of the three objects, bearing in mind that heavier object sinks and lighter object floats. Picture pouring liquid A into a cylinder container liquid B, the answer option is (2)

Image 5
In the end, P and R are empty, Q has 200ml of water.S has 200ml of water, assuming equal pressure acting on surfaces of water and equal flow rates.Container S which is bigger and containing the same amount of water is further away from the fulcrum.
Therefore option (1) is logical.

Image 6
The basic principle is when the effort moves a longer distance, you require less of it.
Hence in descending order, E2, E1 and E3, option (3) is right.

Last image.
Air has no fixed shape and volume. It expands to take up the shape of the container. Option (1) is correct.

[Dharma]

Hi Tianzhu,


For Qn 22, the ball rotates in a clockwise direction towards the boy. Therefore at the point of contact of the ball w/ the ground, the force of motion acts along direction (1). Friction opposes motion, and therefore will act along (3). This is same for wheels of a vehicle moving.

On the other hand, if the ball is replaced with a box that is being pushed towards the boy, the direction of motion of the box is along (3) and the friction acts along (1)

[tianzhu]

Dharma:

Hi Tianzhu,


For Qn 22, the ball rotates in a clockwise direction towards the boy. Therefore at the point of contact of the ball w/ the ground, the force of motion acts along direction (1). Friction opposes motion, and therefore will act along (3). This is same for wheels of a vehicle moving.

On the other hand, if the ball is replaced with a box that is being pushed towards the boy, the direction of motion of the box is along (3) and the friction acts along (1)

Hi, Dharma, you're right.I'll amend the answer.

That's two points in the bag,Thank you for the correction.

But this question touches on rolling friction which may not be in primary science syllabus.

[Drdj]

Dear tianzhu and dharma,


Thanks so much !! Appreciate your detailed explanations !!
Have scanned some further queries from various sources - hope you can help me with them - apologies for the many attachments, as I'm not sure how to do it all in 1 !!
Thanks again
http://www.postimage.org/image.php?v=PqmECgr

http://www.postimage.org/image.php?v=PqmEELA

http://www.postimage.org/image.php?v=PqmEHfJ

http://www.postimage.org/image.php?v=PqmEJKS

http://www.postimage.org/image.php?v=PqmEMf0

[Drdj]

Dear all,


Further queries Thanks in advance
http://www.postimage.org/image.php?v=gx1amC99

http://www.postimage.org/image.php?v=gx1amEEi

http://www.postimage.org/image.php?v=gx1amH8r

http://www.postimage.org/image.php?v=gx1amJDA

http://www.postimage.org/image.php?v=gx1amM7J

[tianzhu]

Hi Drdj


Could you help to provide the sources of your questions eg ACS P6 Sci Q35 SA2 2008?

It appears to me that the questions are from different levels? Just curious, are you a parent or student?

The scanned image may be slightly blurred and small and it may helpful to refer to the originals from http://www.wendykoh.com. Otherwise, it's very taxing for an old man like me to read.

[Dharma]

Drdj:

Dear tianzhu and dharma,


Thanks so much !! Appreciate your detailed explanations !!
Have scanned some further queries from various sources - hope you can help me with them - apologies for the many attachments, as I'm not sure how to do it all in 1 !!
Thanks again

http://www.postimage.org/image.php?v=PqmEELA

Dear Drdj,

Q4) Volume of air will be 500cm3 and 300cm3 in Flask A and B respectively.
Air does not have a definate volume and will spread to occupy the whole container it is in. The capacity of Flask A is 500cm3, so no matter how much air is pumped in, air will compress to occupy the capacity of the flask.

As for flask B, there is 200cm3 of water in it which cannot be compressed. So, air can only occupy the balance 300cm3 space in the flask.

[Dharma]

Drdj:

Dear tianzhu and dharma,


Thanks so much !! Appreciate your detailed explanations !!
Have scanned some further queries from various sources - hope you can help me with them - apologies for the many attachments, as I'm not sure how to do it all in 1 !!
Thanks again

http://www.postimage.org/image.php?v=PqmEHfJ

Air will compress to occupy the max. space in the jar (200cm3)

[Dharma]

Drdj:

Dear tianzhu and dharma,


Thanks so much !! Appreciate your detailed explanations !!
Have scanned some further queries from various sources - hope you can help me with them - apologies for the many attachments, as I'm not sure how to do it all in 1 !!
Thanks again

http://www.postimage.org/image.php?v=PqmEJKS

Q46
a) To find out how different temperatures of water in which the test tube containing yeast with sugar solution is immersed affect the amount of CO2 produced by the yeast.

b) 60 degrees celcius.

c) Sorry, I cant read the Qn