Biology; Chemistry; Physics: Post your doubts here!

[fatima0000]

density of water is 1000 kg/m3 or 1 kg/m3????

 

[usama321]

density of water is 1000 kg/m3 or 1 kg/m3????

i am not sure about this, but thinking logically, 1 kg seems a bit too less in one metre cube, so it should be 1000kg/m3

 

[Saad Mughal]

(f) recognise and use the conventions and symbols contained in ‘Signs, Symbols and Systematics’,
Association for Science Education, 2000.
this is point i read in physics syllabus . i wanna know that what does it mean??? help requiredd

There are several units for everything, for example: mass has units, pounds, grams, ounces.
But we use standard international units called SI units.
This is what is meant by this part.
You should know that, length (m), mass (kg), speed (m/s) and so on...
You should also know that deci is 10^-1 of the basic unit, centi is 10^-2, milli is 10^-3, kilo is 10^3 and mega is 10^6.
Hope that helps.

 

[fatima0000]

Road condition: If the road is wet, friction would be less between the road and the tyres as the surface is slippery. If it is dry, there would be more friction.

Tyre surface: If the surface of the tyres is smooth, there would be less friction. this usually happens if the tyres are old. If there are treads or tracks in the tyres there would be more friction. Similarly to the road, if they are wet, there would be less frction.

Breaking force: If the breaking force is more, than there should be more friction in the tyres and brakes.

Braking distance: Braking distance is the distance covered by the car while the brakes are being applied. Don't know what to write in this one. maybe if the breaking distance is more, than the friction is lesser compared to a shorter braking distance?

Thinking distance: It is the distance covered by the body, during which the driver decides to apply the brake. Don't know what it has to do with friction

Stopping distance: ?

Well in all the above, where there is more friction the vehicle would of course stop faster, and if there is less friction, it would be the opposite. E-g a wet road could cause an accident, similarly old and worn out tyres can cause an accident too etc

what about braking , thinking, and stopping distance????
dont you have any idea about friction in them?

 

[Saad Mughal]

density of water is 1000 kg/m3 or 1 kg/m3????

It's 1000 kg/m^3.

 

[fatima0000]

There are several units for everything, for example: mass has units, pounds, grams, ounces.
But we use standard international units called SI units.
This is what is meant by this part.
You should know that, length (m), mass (kg), speed (m/s) and so on...
You should also know that deci is 10^-1 of the basic unit, centi is 10^-2, milli is 10^-3, kilo is 10^3 and mega is 10^6.
Hope that helps.

should we know about nano as well??..

 

[Saad Mughal]

should we know about nano as well??..

There is no use of it (in terms) for Physics/Chemistry, but you should know that nano is smaller than milli, micro units.

 

[usama321]

what about braking , thinking, and stopping distance????
dont you have any idea about friction in them?

can't think what friction has to do with thinking distance. I don't know what specifically could be related to friction while talking about distance. All i can think is that if there is less distance covered, then there should be more friction in the system in some form

 

[Saad Mughal]

Road condition: If the road is wet, friction would be less between the road and the tyres as the surface is slippery. If it is dry, there would be more friction.

Tyre surface: If the surface of the tyres is smooth, there would be less friction. this usually happens if the tyres are old. If there are treads or tracks in the tyres there would be more friction. Similarly to the road, if they are wet, there would be less frction.

Breaking force: If the breaking force is more, than there should be more friction in the tyres and brakes.

Braking distance: Braking distance is the distance covered by the car while the brakes are being applied. Don't know what to write in this one. maybe if the breaking distance is more, than the friction is lesser compared to a shorter braking distance?

Thinking distance: It is the distance covered by the body, during which the driver decides to apply the brake. Don't know what it has to do with friction

Stopping distance: ?

Well in all the above, where there is more friction the vehicle would of course stop faster, and if there is less friction, it would be the opposite. E-g a wet road could cause an accident, similarly old and worn out tyres can cause an accident too etc

what about braking , thinking, and stopping distance????
dont you have any idea about friction in them?

Braking distance is the distance traveled by the car when the brakes are applied. In context, the greater the braking FORCE applied the more quickly the car will stop. It is related to friction in the manner that the larger the braking force, the higher the frictional resistive force (which helps the car stop).
Thinking distance, also known as reaction time, has nothing to do with friction, it solely depends on the driver and how long he takes to react to apply the brakes.
Stopping distance is the total distance traveled by the car during this period, it is the sum of the thinking and braking distance.

 

[fatima0000]

Braking distance is the distance traveled by the car when the brakes are applied. In context, the greater the braking FORCE applied the more quickly the car will stop. It is related to friction in the manner that the larger the braking force, the higher the frictional resistive force (which helps the car stop).
Thinking distance, also known as reaction time, has nothing to do with friction, it solely depends on the driver and how long he takes to react to apply the brakes.
Stopping distance is the total distance traveled by the car during this period, it is the sum of the thinking and braking distance.

but i doubt about braking distance because i think you have written about braking force above..
would not it be like greater the braking distance smaller would be the friction and vice versa..

 

[Saad Mughal]

but i doubt about braking distance because i think you have written about braking force above..
would not it be like greater the braking distance smaller would be the friction and vice versa..

Braking force is applied to the braking pads of the car, they make the wheels stop rotating but because of inertia, the car doesn't stop instantly, the frictional forces acting on the car help it to stop (acting opposite to the direction of motion).

 

[fatima0000]

(d) describe how to verify the principle of moments.
explaination???

 

[Usama Jawad]

Can anyone tell me about precautions when performing titrations?
I know that eye should be level with meniscus curve and there should be no impurities but are there any other?
plz reply

 

[Saad Mughal]

(d) describe how to verify the principle of moments.
explaination???

See attached picture.
The weights are moved along the scale and it seen that the plank is only in equilibrium when the clockwise and anticlockwise moments are balanced. This experiment verifies the principle of moments.

 

[Saad Mughal]

Can anyone tell me about precautions when performing titrations?
I know that eye should be level with meniscus curve and there should be no impurities but are there any other?
plz reply

Precautions:
- Parallax error should be avoided. Eye placement should be correct when taking readings.
- All solutions (acids and alkalis) should be pure, impurities (such as indicators) should not be present (when preparing salts).
- The burrette should be clean and pure to avoid concentration errors.
- Care must be taken when handling/using acids/alkalis, they can cause skin burns.
- As acid (or alkali in some cases) is added to the flask, the flask should be regularly shaken to make sure that the mixture mixes properly.
- Care must be taken when adding the acid (or alkali) to the titration flask. It must be added drop by drop (not at once) so that the end point can be noted.
- All equipment, such as burrette, flask and pipette should be in proper condition. No leakages/impurities should be present.
- When the salt is prepared, the solution should be heated gently (not vigorously) to allow the water to evaporate from the solution.
Well, that's all I can think of right now. Hope that helps.

 

[papajohn]

Precautions:
- Parallax error should be avoided. Eye placement should be correct when taking readings.
- All solutions (acids and alkalis) should be pure, impurities (such as indicators) should not be present (when preparing salts).
- The burrette should be clean and pure to avoid concentration errors.
- Care must be taken when handling/using acids/alkalis, they can cause skin burns.
- As acid (or alkali in some cases) is added to the flask, the flask should be regularly shaken to make sure that the mixture mixes properly.
- Care must be taken when adding the acid (or alkali) to the titration flask. It must be added drop by drop (not at once) so that the end point can be noted.
- All equipment, such as burrette, flask and pipette should be in proper condition. No leakages/impurities should be present.
- When the salt is prepared, the solution should be heated gently (not vigorously) to allow the water to evaporate from the solution.
Well, that's all I can think of right now. Hope that helps.

washed the apparatus with tap water then with distilled water Am i right?

 

[TheStallion-Reborn]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s12_qp_22.pdf
question 9 part a! help please

 

[TheStallion-Reborn]

Precautions:
- Parallax error should be avoided. Eye placement should be correct when taking readings.
- All solutions (acids and alkalis) should be pure, impurities (such as indicators) should not be present (when preparing salts).
- The burrette should be clean and pure to avoid concentration errors.
- Care must be taken when handling/using acids/alkalis, they can cause skin burns.
- As acid (or alkali in some cases) is added to the flask, the flask should be regularly shaken to make sure that the mixture mixes properly.
- Care must be taken when adding the acid (or alkali) to the titration flask. It must be added drop by drop (not at once) so that the end point can be noted.
- All equipment, such as burrette, flask and pipette should be in proper condition. No leakages/impurities should be present.
- When the salt is prepared, the solution should be heated gently (not vigorously) to allow the water to evaporate from the solution.
Well, that's all I can think of right now. Hope that helps.

height of awesomeness! ur sources??

 

[AhsanAfzal]

conventional current (positive to negative) it is coming frm behind the transformer to make a loop

 

[papajohn]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s12_qp_22.pdf
question 9 part a! help please

This question came in my mock exam and i draw this diagram. Dont know yet about correct diagram.