Q&A - PSLE Science

[tianzhu]

Living Together/Food Web


Thank you for your help.

What's your take on part(b)?

http://farm4.static.flickr.com/3558/3553015310_8ae7f582f7_o.jpg\">

[tianzhu]

Heat


Thank you for your help.

For part(a) ---It's not a fair test.The areas of exposed surfaces to the surroundings as well as the area of contact between the ice and the materials affect the time taken for the ice to melt.What's your view?

For part(b) --- The temperature of the ice remains the same, while the temperature of material X decreases.Do you agree?

http://farm4.static.flickr.com/3395/3553015402_89930b555e_o.jpg\">

[tianzhu]

Energy


Thank you for your help.

Based on the information in the question, can we tell how high the rubber ball will reach after bouncing off the concrete surface?
(2) or (3) or anywhere between(2) and (3) are logical answers.Some of the KE has been converted into heat and sound energy, hence the ball will not rebound to its original position.

http://farm4.static.flickr.com/3638/3552206045_f1f6136f0b_o.jpg\">

[ChiefKiasu]

tianzhu:

...Part (b) --- Without any doubts, Gear Y will turn more rounds as its diameter is smaller than Gear Z.But, how many more?Could we tell based on the information given in the question?

...

Yes we can, by counting the number of spokes on the gears.
Gear Y = 10
Gear Z = 16
Ratio = 16:10 => if Gear Z turns 1 round, Gear Y would have turned 1.6 rounds.

So if Gear Z turns 5 rounds, Gear Y would have turned 5x1.6=8 rounds.

[tianzhu]

Thank you for your help.


http://farm4.static.flickr.com/3314/3561514633_fbc309c8be_o.jpg\">

[Drdj]

[Moderator's note: Topics merged.]


http://www.postimage.org/image.php?v=Pq12Ooo0

Hi, can you help me explain why the given answer is option (4)?
Thanks.

[tianzhu]

Drdj:

[Moderator's note: Topics merged.]


http://www.postimage.org/image.php?v=Pq12Ooo0

Hi, can you help me explain why the given answer is option (4)?
Thanks.

Hi
Let us recap

In PSLE science, students are not taught how to determine the polarity of an electromagnet. They learned that an electromagnet is made when you coil an electric wire a few times around a magnetic material.
Copper is a non magnetic material.(MPH PSLE Science Guide pg 64)
For magnets, like poles attract and unlike poles repel. (MPH PSLE Science Guide pg 66)

Consider (1) --- The bulb lights up as a closed circuit is formed. The magnet may move to the left if unlike poles are facing one another.
(1)is a logical answer.

Consider(2) ---The copper remains in the same position as it is non magnetic. The magnet may move to the right if like poles are facing one another.Hence (2) is also correct.

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.

Therfore option (1) and (2) are logical.Where is this question from?

[Drdj]

It's from Tao Nan SA1 2008 paper.

Thanks for your quick response

[Drdj]

It's from Tao Nan SA1 2008 paper.

Thanks for the quick response

tianzhu:

Drdj:

[Moderator's note: Topics merged.]

http://www.postimage.org/image.php?v=Pq12Ooo0

Hi, can you help me explain why the given answer is option (4)?
Thanks.

Hi
Let us recap

In PSLE science, students are not taught how to determine the polarity of an electromagnet. They learned that an electromagnet is made when you coil an electric wire a few times around a magnetic material.
Copper is a non magnetic material.(MPH PSLE Science Guide pg 64)
For magnets, like poles attract and unlike poles repel. (MPH PSLE Science Guide pg 66)

Consider (1) --- The bulb lights up as a closed circuit is formed. The magnet may move to the left if unlike poles are facing one another.
(1)is a logical answer.

Consider(2) ---The copper remains in the same position as it is non magnetic. The magnet may move to the right if like poles are facing one another.Hence (2) is also correct.

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.

Therfore option (1) and (2) are logical.Where is this question from?

[tianzhu]

Thank you for your help.


Why does the temperature not rise until all the ice melted into water? Where does the energy for melting the ice come from?

I did a search using Google/Yahoo and came across an interesting article.
http://www.scientificpsychic.com/mind/colddrink1.html

There is latent (hidden) heat of fusion during the melting of ice when the temperature remains at 0 degree Celsius.