tianzhu:

Dharma:

B & C - if end of the electromagnet facing the magnet and the magnet are like poles, the magnet will move to the right...Magnetic force of repulsion. If the end of the electromagnet facing the magnet and the magnet are unlike poles, the magnet will move to the left ...Magnetic force of attraction....Therefore B and C are likely observations.
I will go for (4) - B,C and D only

Hi Dharma

Yes, B and C are likely observations, but they do not occur at the same time.

Consider (3) ---The magnet either moves to the left or right.B and C cannot happen at the same time.Therefore (3) is out.

Consider(4) ---For the same reason as (3), this option is also out.

Hi Tianzhu,

Maybe if \"all possible observations\" is used in the qn then ...will be clearer.

tianzhu:

Thank you for your help.


RGPS SA1 2008
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Hi Tianzhu,

U can also solve it this way

Jane can complete 1/10 of the strings in 1 day
Sharon can complete 1/18 of the strings in 1 day

If Jan takes N days, Sharon will take (14-N)days to complete the work.

Therefore,

N/10 + (14-N)/18 = 1

N= 5

Jane took 5 days

Dharmaratnam:

tianzhu:

Thank you for your help.

http://www.wendykoh.com/08/primary6-nanyangca1-science.pdf
The answer(ws) to the last part of the question is Potential energy --> Electrical Energy.Please help to explain why.
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http://farm4.static.flickr.com/3318/3449160899_a9bf5c4f6d_o.jpg\">

The answers for part (c) and (d). I don't think that the ws answer is correct.

# Chemical potential energy is converted to electrical energy which will be converted to light, sound and heat energy when switches A,B,C, and A,B,C and D are closed.

Hi Tianzhu,

In a parallel circuit, the electric current can flow along several paths. The amount of electric current along each path will be same. If we replace the buzzer and nichrome wire with similar bulbs as the one in the circuit, each of the bulbs will light up as bright as the first one and brightness of the bulbs remains the same even if new paths with bulbs are added.

Therefore, coming back to the qn, when switches A,B,C,and D are closed, the bulb will light up as brightly as before, the buzzer will sound as loud as before and the nichrome wire will glow the same as before.

I still think that potential changes to electrical energy to light + sound + heat.

# Pls do not look into it too deeply....resistance is NOT taught in P5/P6..so don't worry too much about it.

So, even if switch D is closed, electric current will still flow through all 4 loops ...therefore answers to (c) and (d) are the same. Think the examiner just trying to test the basic understanding of the child with regards to parallel circuits in this case.

tianzhu:

Thank you for your help.

http://www.wendykoh.com/08/primary6-nanyangca1-science.pdf
The answer(ws) to the last part of the question is Potential energy --> Electrical Energy.Please help to explain why.
http://farm4.static.flickr.com/3408/3449160885_4227ce975c_o.jpg\">
http://farm4.static.flickr.com/3318/3449160899_a9bf5c4f6d_o.jpg\">

The answers for part (c) and (d). I don't think that the ws answer is correct.

# Chemical potential energy is converted to electrical energy which will be converted to light, sound and heat energy when switches A,B,C, and A,B,C and D are closed.

ksmama:

Hi, I think the paper bag question is both a test of materials and structure of a cell.

a) Set up A consists of a paper bag. Paper is thin and and not strong. It is thus unable to withstand the increase in pressure when air is pump into it and ends up bursting. On the other hand in set B, the paper bag is placed in a plastic bag. Plastic is a strong material and is able to support and protect the paper bag inside it. When air is pumped into this bag, the increased pressure inside the paper bag, the bag is cushioned and supported by the plastic bag outside it and therefore, it does not burst.

b) the animal cell has only a thin cell membrane as its covering. It is not strong and is not able to withstand the increase in pressure when water is pumped into it and ends up bursting. The plant cell, on the other hand, has an inner cell membrane, supported by an outer rigid cell wall. When water is pumped into the plant cell, the cell wall will protect and support the cell when its inner pressure increases and thus prevents it from bursting

Dear ksmama,

You certainly have given a very clear explanation. Thanks.

Tianzhu, somehow I was not sure of what the question was trying to say about the paper bags. The 1st sentence talked about 2 paper bags. The 2nd sentence mentioned that there was a thick plastic bag that was the same size and shape of the paper bag.

The picture however, shows a plastic bag and another with paper bag inside the plastic bag.

I was also confused ........

fxchow:

Hi,


Pls help to solve this speed question. TIA

A tiger and a leopard are 60km apart.
The tiger runs at a speed of 55km/h.
At the same time, the leopard runs towards the tiger at a speed of 25km/h.
How much further will the tiger have run than the leopard when the two animals meet?

For fixed time taken, the ratios of speed and distance of tiger to leopard are ..
\tTiger\tLeopard
Speed\t11 :\t5
Distance\t11 :\t5

16units =60km
2units = 7.5km
6units = 22.5km

The tiger would have run 22.5km further than the leopard when they meet.

tianzhu:

Thank you for your time.


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One way I can think of is to increase the height of the metal stand carrying the ball.Another way is to use a bigger metal ball(increased mass)
But, how about moving the fulcrum closer to the wooden disc.Does it helps?

My answer will be as follows..
(a) Move the fulcrum closer to the load (wooden disc)

(b) The metal ball drops on the wooden plank with the same force but a greater moment is created due to the increase in the effort arm. Since the load arm is shorter now, the wooden disc will be thrown up a higher distance with a greater force. It will then be able to hit and sound the drum

Hi Small,


Now that you are aware that AB can be found using at least 2 methods … the examiner can go 1 step further to ask for area of FED.