Q&A - PSLE Science

[Robertpattinsonidle]

my answer is 3. answer key says 2. any explanantion? http://i46.tinypic.com/fadmj6.jpg\">

[charsen]

Robertpattinsonidle:

my answer is 3. answer key says 2. any explanantion? http://i46.tinypic.com/fadmj6.jpg\">

Hi
The answer is 3.No doubt that water conducts very little heat to the ice since water is a poor conductor of heat.But before the heat reaches the water first,the test tube would gain heat and heat would travel throughout the test tube.Thus,heat also travles to the bottom of the test tube.Since the ice is wrapped with wire gauze,it is an insulator of heat and prevents ice from melting from the boiling water.
Please confirm the answer.
Charsen.

[charsen]

ximinful:

Hi charsen, please help me some other science qns:

-Why doesn't the bird get electrocuted when it stands on the power line?
-Are the magnetism of a ring and button magnet even?
-what do the organisms compete for in the pond?(when overcrowded)
-what is the energy conversion when someone flies the kite?
-do 2 objects have friction when they are in contact with each other?
-would a heavier bag fall faster than a lighter bag from the same level?how about an object greater in width?
-will expansion cause an increase in mass of an object?
-how do animals get oxygen underground?
-what are the factors for decomposition to occur?
-does oxygen pass thru the circulatory and digestive system?

Ps. Sorry for \"bombarding\" u with so many questions but my science isn't that fantastic. Thanks in advance!

Ive tried my best to answer. Let me know if you find any of them wrong.
Q1 Why doesn't the bird get electrocuted when it stands on the power line?
Birds do not get electrocuted when it stands on the power line. Electricity passes through CLOSED circuit. When the bird sits on the powerline, it only touches only point and does not complete the circuit. Usually one end of the electric circuit of powerlines will be buried under earth. As long as any part that conducts electricity does not touch the end of circuit in earth, should be safe.

Q2Are the magnetism of a ring and button magnet even?
No.
The attraction of a magnet is strongest at the poles. Both button, ring magnets have poles and hence the magnetism is not even.

Q3 what do the organisms compete for in the pond?(when overcrowded)
Pond organisms compete for sunlight, space and oxygen.

Q4 what is the energy conversion when someone flies the kite?

Q5 do 2 objects have friction when they are in contact with each other?
Yes. Friction exists between 2 objects in Contact. Note: (From PSLE revision guide, Friction occurs in both stationary object (static friction) and moving objects (kinetic friction).

Q7 will expansion cause an increase in mass of an object?
No. Expansion of matter does not cause an increase in mass. Mass of an object is constant regardless of where the object is. Only when we add or take away some of the matter, the mass would change.

Q8 how do animals get oxygen underground?
Underground (Burrowing) animals mix air with soil as they burrow and obtain oxygen from the air in soil.

Q9 what are the factors for decomposition to occur?
Under favourable temperature, Air and moisture decomposition occurs.

Q10 does oxygen pass thru the circulatory and digestive system?
Oxygen pass through circulatory but not digestive system. Oxygen is exchanged between the cells of the body through the blood vessels (which are part of circulatory system)

[verykiasumummy]

charsen:

Robertpattinsonidle:

my answer is 3. answer key says 2. any explanantion? http://i46.tinypic.com/fadmj6.jpg\">

Hi
The answer is 3.No doubt that water conducts very little heat to the ice since water is a poor conductor of heat.But before the heat reaches the water first,the test tube would gain heat and heat would travel throughout the test tube.Thus,heat also travles to the bottom of the test tube.Since the ice is wrapped with wire gauze,it is an insulator of heat and prevents ice from melting from the boiling water.
Please confirm the answer.
Charsen.

hi, sorry but ans should be 2, not 3. the wire gauze just prevents heat from reaching the ice too easily, in other words, it reduces the heat travelling to the ice, hence ice melts slower. but A states the wire gauze prevents heat from reaching the ice so technically the statement is wrong.

my ds last yr got caught at a similar question. if use prevent, must use with \"prevent....easily...\" if not use \"reduce....\" (den dun need to put easily)

hope it clarifies... i'm just sharing what the sci teacher says...

[Robertpattinsonidle]

[quote="charsen"][quote="ximinful"]

-what is the energy conversion when someone flies the kite?



Q4 what is the energy conversion when someone flies the kite?

i think u missed out on tht qsn. its actually
Kinetic energy [in wind] to gravitational potential energy [in above the ground kite] to kinetic energy in flying kite. if there are additional boxes u can say that heat is also produced due to air resistance. thanks. hope it helps.
cheers!

[Robertpattinsonidle]

verykiasumummy:

using another magnet to chk if it repels is not required to confirm if they have become temperary magnets, (only when u need to confirm an object is a magnet, as in permanent magnet) because temporary magnets are just for short term, so the repulsion may not be guaranteed.

i tried that at home.

[Robertpattinsonidle]

Robertpattinsonidle:

verykiasumummy:

using another magnet to chk if it repels is not required to confirm if they have become temperary magnets, (only when u need to confirm an object is a magnet, as in permanent magnet) because temporary magnets are just for short term, so the repulsion may not be guaranteed.

i tried that at home.

it doesnt actually work.

[Robertpattinsonidle]

Robertpattinsonidle:

Robertpattinsonidle:

[quote=\"verykiasumummy\"]using another magnet to chk if it repels is not required to confirm if they have become temperary magnets, (only when u need to confirm an object is a magnet, as in permanent magnet) because temporary magnets are just for short term, so the repulsion may not be guaranteed.

i tried that at home.

it doesnt actually work.[/quote]i did about 50 strokes but the temporary magnet still is not as strong enough as needed in order to repel a magnet. thanks
Cheers! :roll:

[charsen]

verykiasumummy:

charsen:

[quote=\"Robertpattinsonidle\"]my answer is 3. answer key says 2. any explanantion? http://i46.tinypic.com/fadmj6.jpg\">

Hi
The answer is 3.No doubt that water conducts very little heat to the ice since water is a poor conductor of heat.But before the heat reaches the water first,the test tube would gain heat and heat would travel throughout the test tube.Thus,heat also travles to the bottom of the test tube.Since the ice is wrapped with wire gauze,it is an insulator of heat and prevents ice from melting from the boiling water.
Please confirm the answer.
Charsen.

hi, sorry but ans should be 2, not 3. the wire gauze just prevents heat from reaching the ice too easily, in other words, it reduces the heat travelling to the ice, hence ice melts slower. but A states the wire gauze prevents heat from reaching the ice so technically the statement is wrong.

my ds last yr got caught at a similar question. if use prevent, must use with \"prevent....easily...\" if not use \"reduce....\" (den dun need to put easily)

hope it clarifies... i'm just sharing what the sci teacher says...[/quote]Hi
Thank you for the sharing.I learnt something new today.
Charsen.

[Zhu99]

Robertpattinsonidle:

my answer is 3. answer key says 2. any explanantion? http://i46.tinypic.com/fadmj6.jpg\">

The answer key 2 is correct.

The purpose of the wire gauze is to keep the ice at the bottom of the test tube. (Wire gauze is a good conductor of heat).

The experiment basically shows that water is a poor conductor of heat. [Note: Water is a good conductor of electricity. Normally a good conductor of heat is also a good conductor of electricity.]