Q&A - PSLE Science

[Sun_2010]

its888me:

ACS 2011 Prelim Paper, Section B, Q41:


http://i49.tinypic.com/2h3btzd.jpg\">
(b) Farmer Amos noticed that his maize plantation has been infested by rats. Without introducing any new species into the above food web, suggest a suitable and sage method that can help him overcome this problem.

Marking Scheme:
- Introduce owls into the community (1)
- Introduce snakes (0)
- Introduce snakes & owls (0)

Why is \"Introduce snakes\" getting a 0 marks since snakes will eat up the rats?

TIA!

I think the highlighted word is safe .
That is why cannot be more snakes ?

[charsen]

its888me:

ACS 2011 Prelim Paper, Section B, Q41:


http://i49.tinypic.com/2h3btzd.jpg\">
(b) Farmer Amos noticed that his maize plantation has been infested by rats. Without introducing any new species into the above food web, suggest a suitable and sage method that can help him overcome this problem.

Marking Scheme:
- Introduce owls into the community (1)
- Introduce snakes (0)
- Introduce snakes & owls (0)

Why is \"Introduce snakes\" getting a 0 marks since snakes will eat up the rats?

TIA!

Hi
In my point of view,introducing the snakes would harm other useful animals in the plantation.Not only that,the owl population would also increase,so you can say that both populations would compete for food,which results in the decrease in the number of snakes only.
cheers
Cheers

[elkniwt]

Hi,


Need help on this qn from CHS prelim :

http://i46.tinypic.com/1zp03fb.jpg\">

Answer in answer key is (2). dd's ans is (1) ?? (I think ans key is wrong, need some advices. Thanks!) :?:

[Robertpattinsonidle]

there is only one hole for both water and air to escape. hence the hole is not enough for the air to leave and enter to push the water out. this results in blockage and hence the milk flows out slowly. the second part to this qsn is how to increase flow of milk so u can say that poke another hol and the explanation is that in one hole milk can flow out and in the other air can enter to occupy the space and also push the milk out hence increasing rate of milk flow.

[Chan09]

Need some help as don’t understand why this is false?


When a ball reaches its max height, the force of gravity acting on the ball is the greatest.

Tks

[fightingmom]

Chan09:

Need some help as don't understand why this is false?


When a ball reaches its max height, the force of gravity acting on the ball is the greatest.

Tks

The force of gravity remains the same as it is the same force that pulls everything down to earth. No matter what is the height or weight of an object, the force of gravity will be the same.

NOTE: Don't confuse with gravitational potential energy (GPE) which is affected by height and weight.

Hope it helps.

[Fat Mama]

elkniwt:

Hi,


Need help on this qn from CHS prelim :

http://i46.tinypic.com/1zp03fb.jpg\">

Answer in answer key is (2). dd's ans is (1) ?? (I think ans key is wrong, need some advices. Thanks!) :?:

Hi,

Ans (2) is correct.

Reason being marbles are round and hv gaps bet them. When liquid is pour in, it will fill up the gaps of the marbles. So vol of gas should be more than 700 which is (2) 750

[elkniwt]

Fat Mama:

Hi,

Ans (2) is correct.

Reason being marbles are round and hv gaps bet them. When liquid is pour in, it will fill up the gaps of the marbles. So vol of gas should be more than 700 which is (2) 750

Hi Fat Mama,

Thanks for taking time to reply

When the question says the total volume of marbles is 100 cm3, we thought it meant the total volume of the marbles without the gaps. :? (Cos usually, if we say volume of 1 marble is 10 cm3, volume of 10 marbles will be 100cm3, we don't factor in the gaps right?? )

[Robertpattinsonidle]

elkniwt:

Fat Mama:

Hi,

Ans (2) is correct.

Reason being marbles are round and hv gaps bet them. When liquid is pour in, it will fill up the gaps of the marbles. So vol of gas should be more than 700 which is (2) 750

Hi Fat Mama,

Thanks for taking time to reply

When the question says the total volume of marbles is 100 cm3, we thought it meant the total volume of the marbles without the gaps. :? (Cos usually, if we say volume of 1 marble is 10 cm3, volume of 10 marbles will be 100cm3, we don't factor in the gaps right?? )

this is becos the pebbles dont have definite shape. If we fill a bucket with 10 pebbles or stones, there are still air spaces cuz pebbles cant be compressed and have definit shape

[Alarmchain]

Total Vol in Bottle = 1000cc


Substances that cannot be compressed that are added:
a) Marbles, Vol = 100cc
b) Substance B, Vol = 200cc
Therefore, total volume occupied by substances that cannot be compressed = 300cc

From here, total available space in bottle becomes 1000cc - 300cc = 700cc

Substance D is compressible.
Original Vol of D = 700cc
Added vol of D = 100cc
Total Vol of D = 800cc

Despite D having a total vol of 800cc, the available space in bottle is still 700cc. So, substance D must compress itself to fit into the available 700cc volume. Hence, I think 700cc is the correct answer.