Q&A - PSLE Science

[Dharma]

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\">

Hi Tianzhu,

I don't think it is possible to accurately predict the exact position the ball will bounce back after hitting the concrete surface....for me ...somewhere midway between Point 1 and Point 2 up to Point 3 will be reasonable....although I think it is likely to be closer to Point 2....as concrete is hard and this will enable the ball to bounce back high ...but definately not to Point 1.

[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.

[Dharmaratnam]

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.

[Drdj]

[Moderator's note: Topics merged.]


http://www.postimage.org/image.php?v=Pq1EkKm0

Hi there, I have another query on this question - it's from the PSLE 5 year series ...
The answer given is distance y will decrease.
Iron ring will be attracted to magnet , but gravitational force exerted by combined weight of the iron ring and magnet A is greater than that of magnet A alone, reducing the distance y.

My question is : How do you know the gravitationl force is greater than the magnetic force of repulsion (which causes distance y in the first place?)

Thanks in advance.

[jedamum]

discuss psle science http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=1727&start=0.

pls do a search before starting a thread.
TQ

[Drdj]

jedamum:

discuss psle science http://www.kiasuparents.com/kiasu/forum/viewtopic.php?t=1727&start=0.

pls do a search before starting a thread.
TQ

My apologies. I was at Pg 12 of the link you mentioned, but i clicked on 'New Post' instead - this seems to be the incorrect option - I should probably click 'Quote' to any of the posts. Sorry about that.

[jedamum]

Drdj:

but i clicked on 'New Post' instead - this seems to be the incorrect option - I should probably click 'Quote' to any of the posts. Sorry about that.

seems like a lot of newbie make this type of mistake. must be too excited/anxious...

[tianzhu]

Hi


To avoid starting a new thread, you have to hit post reply.This will keep you in the existing thread.

From MPH PSLE Science Guide pg 194/195

Weight is the amount of gravitational force acting on an object. It tells us how heavy an object is.
There are two types of magnetic forces — attraction and repulsion.

In this question, the force of repulsion is in action. It keeps the two magnets at a distance y from one another at the beginning stage. Iron is magnetic and will be attracted to magnet A. The combined forces of the magnet A and the piece of iron ring will reduce the distance y.

To see it in another way, imagine the distance y being replaced by a spring. The two magnets are replaced by two pieces of non magnetic materials such as plastic A and B. You put an additional weight on top of A. Will the spring be compressed as compared to its initial position?

[Drdj]

tianzhu:

Hi


To avoid starting a new thread, you have to hit post reply.This will keep you in the existing thread.

From MPH PSLE Science Guide pg 194/195

Weight is the amount of gravitational force acting on an object. It tells us how heavy an object is.
There are two types of magnetic forces --- attraction and repulsion.

In this question, the force of repulsion is in action. It keeps the two magnets at a distance y from one another at the beginning stage. Iron is magnetic and will be attracted to magnet A. The combined forces of the magnet A and the piece of iron ring will reduce the distance y.

To see it in another way, imagine the distance y being replaced by a spring. The two magnets are replaced by two pieces of non magnetic materials such as plastic A and B. You put an additional weight on top of A. Will the spring be compressed as compared to its initial position?

Thanks for the helpful analogy - sure clears things up
I was of the impression the distance y will increase, since the iron will be attracted to the magnet. However, since the question assumes they are identical, I reckon that distance y will decrease.

[Dharma]

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\">

Hi Tianzhu,

Part (a) - The only variable that changes should be the type of material used (Material X and Material Y). All other variables (e.g. how the ice blocks are placed on the 2 materials) must remain the same.

Part (b) - I agree with your answer