Q&A - PSLE Science

[atutor2001]

Hi Pita, below are my comments.

[quote].....Therefore, air outside the flask in the plastic tube does not have to enter the flask to fill up the space. [/quote]When the flask expanded, the air in the plastic tube must \"spread out\" into the flask because the tube is connected to the flask. With nothing separating the air in the tube and the flask, these 2 volumes of the air must be considered as 1 whole \"body\".
[quote]Thus, equal forces from both flasks in this case are pushing the water droplet, so it should not move at all [/quote]Since the air in the tube must also \"spread into the flask\" the pressure (force) acting on this side of the ink drop will decrease causing the ink to move towards the expanded flask. As the ink moves, the volume on the side of the expanded flask decreases causing the pressure to increase. At the same time, the the volume of the tube on the other side of the ink drop increases, causing the pressure to decrease. (Therefore, the movement of the ink causes opposite effect to the pressure on the 2 sides) The ink will stop moving when the pressure (force) on both sides of the ink becomes equal again.

[Pita]

Hi atutor2001,


Thank you so, so much for your explanations, really appreciate your help!

[atutor2001]

P5G:

Please help.



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TIA.

This looks like a math question.

4000m - 1000m = 3000m
6 degree - 0 degree = 6 degree

6 degree -> 3000m
1 degree -> 3000/6 = 500m

1000m + 500m = 1500m

I will put 1501m (amended) as the answer because at 1500m the temp is 5 degree but the fish needs a temperature of \"less than 5 degree\".

(quite a bad question)

[P5G]

Please help.


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TIA.

[P5G]

Cockroach:

P5G:

Pease help.


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TIA.

a) A,F
A
b) Gravity and friction
c) Kinetic energy -> heat+ sound

Hi,

Thanks for your answers.

My original answers were the same as yours, but I think they are not correct (see my doubts below) and I could not think of any better answers.

My doubts:
For a) if Kinetic energy is 0, then the car will not have hit the bumper.
[When we drop something from a height, the kinetic energy is the highest when it hits the floor.]

For c), it is funny to me that energy of car hitting the bumper is heat energy and sound energy.

[P5G]

Please help.


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TIA.

[Publica]

Hi,


I have a question regarding melting. We know that the temperature of the melting ice will remain at 0 Deg C until the ice has melted completely. However, will the temperature of the water from the melting ice increase as the ice is still melting as it gains heat from the surrounding air?

Thanks.

[atutor2001]

P5G:

Please help.


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TIA.

(a) She waited for 2 minutes to allow time for heat to travel from the water bath to the water in the test tube so that the temperature of every part of the water in the test tube has reached 20 degree C.

(b) Conducting the experiment in a cool room will improve the accuracy because temperature of the water in the test tube will be quite the same as the temperature in a cool room and this will minimise heat gained or loss by the experiment set-up.

(c) The physical factor needed is warmth

[atutor2001]

Publica:

Hi,


I have a question regarding melting. We know that the temperature of the melting ice will remain at 0 Deg C until the ice has melted completely. However, will the temperature of the water from the melting ice increase as the ice is still melting as it gains heat from the surrounding air?

Thanks.

If the water is still in contact with the ice, the normal answer is NO (for science question) because it is assumed that any gain in heat by the water will flow to the ice and will be used to cause more of the ice to melt.

However, if the water has flown to quite a distance from the ice, it will take time for the heat gain to travel to the ice. Therefore, in reality, melted water that has flown to quite a distance from the ice can actually be more than 0 degree if the environment is very hot.

[Publica]

atutor2001:

Publica:

Hi,


I have a question regarding melting. We know that the temperature of the melting ice will remain at 0 Deg C until the ice has melted completely. However, will the temperature of the water from the melting ice increase as the ice is still melting as it gains heat from the surrounding air?

Thanks.

If the water is still in contact with the ice, the normal answer is NO (for science question) because it is assumed that any gain in heat by the water will flow to the ice and will be used to cause more of the ice to melt.

However, if the water has flown to quite a distance from the ice, it will take time for the heat gain to travel to the ice. Therefore, in reality, melted water that has flown to quite a distance from the ice can actually be more than 0 degree if the environment is very hot.

Hi atutor2001,
Thanks for the prompt reply. That was what my son understood to be but the answer key gave a different answer.