Biology; Chemistry; Physics: Post your doubts here!

[Suchal Riaz]

but isnt it still being produced? question says it is constant

who told u it is produced?
let see velocity and height as it falls.
initially it's velocity is 0 but height is maximum. by equations (k.e=1/2mv² and p.e=mgh) P.E is maximum and Kinetic energy is zero. as it accelerates it's height decrease means P.E is decreasing. velocity increase means K.E is increasing. then it reaches terminal velocity(constant velocity) so P.E is still decreasing as height is decreasing but K.E is constant(not zero but also not changing).
by law of conservation total mass and energy of a system remains constant. so at every moment. K.E+P.E+internal energy=constant. yani jab K.E is not changing the decreasing P.E is changing into Internal energy.

 

[AhsanAfzal]

who told u it is produced?
let see velocity and height as it falls.
initially it's velocity is 0 but height is maximum. by equations (k.e=1/2mv² and p.e=mgh) P.E is maximum and Kinetic energy is zero. as it accelerates it's height decrease means P.E is decreasing. velocity increase means K.E is increasing. then it reaches terminal velocity(constant velocity) so P.E is still decreasing as height is decreasing but K.E is constant(not zero but also not changing).
by law of conservation total mass and energy of a system remains constant. so at every moment. K.E+P.E+internal energy=constant. yani jab K.E is not changing the decreasing P.E is changing into Internal energy.

got it..thnks bro

 

[Suchal Riaz]

got it..thnks bro

no problem

 

[AhsanAfzal]

no problem

parachutist jal nahi jae gaa itni zaada heat sey?

 

[Suchal Riaz]

parachutist jal nahi jae gaa itni zaada heat sey?

kitni heat he
thori se tou hoti he. us mein sound energy bhi he aur sath heat energy mostly air mein jaye gi. as work is done against air resistance.

 

[Saad Mughal]

parachutist jal nahi jae gaa itni zaada heat sey?

On another note; the person could turn into anti-matter because of the heat and vanish into thin air.

 

[AhsanAfzal]

On another note; the person could turn into anti-matter because of the heat and vanish into thin air.

whaaaaaaaaaaaatttttttttttttttttt????????????

 

[Saad Mughal]

whaaaaaaaaaaaatttttttttttttttttt????????????

It's a pun. Don't believe in it.

 

[AhsanAfzal]

It's a pun. Don't believe in it.

how do u do past papers,in mind or in a copy?

 

[Saad Mughal]

how do u do past papers,in mind or in a copy?

I have a book, I solve in it. However, I do the 2011-2012 Past papers from the internet, I write the MCQ's answers on notepad and check them later and I do the theory questions in mind.

 

[Khadija_1234]

http://papers.xtremepapers.com/CIE/...al O Level/Chemistry (5070)/5070_s07_qp_1.pdf
Please explain Q28 and 29

 

[Hskk]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s07_qp_1.pdf
Please explain Q28 and 29

Q28. As you go down the reactivity series, the elements make less stable compounds, among these options, CuO is the compound of the least reactive metal so the answer is B.
Q29. I did this question by elimination. Cu is obviously oxidised because its oxidation state changes from 0 to 2+, as the reaction proceeds, the amount of silver displaced thus deposited will increase so A and B are right, the colour of aq. Cu2+ compounds is blue so D is right, thus C is the answer.

 

[Saad Mughal]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s07_qp_1.pdf
Please explain Q28 and 29

For 28, you can see that a reaction has occurred since a colorless liquid forms on cooling (if a reaction had not occurred the hydrogen would just pass through). Now, you check the possibilities of a reaction occurring. A and D are oxides of more reactive metals than hydrogen, so the reaction won't occur. For C, Magnesium Hydride would be formed which is an ionic compound (we don't know about it much so we can assume this option incorrect). Now, with B, hydrogen displaces the copper and forms steam (g) which is cooled to form water (the colorless liquid).
For 29, it's being done using elimination; since copper does react with AgNO3, it loses electrons to form the positive ions so A is correct. B is correct too since the mass of silver gradually increases as it is being displaced. D is also correct since Copper (II) Nitrate is blue and it will turn the solution blue as well. So, the only incorrect statement is C.

 

[Khadija_1234]

For 28, you can see that a reaction has occurred since a colorless liquid forms on cooling (if a reaction had not occurred the hydrogen would just pass through). Now, you check the possibilities of a reaction occurring. A and D are oxides of more reactive metals than hydrogen, so the reaction won't occur. For C, Magnesium Hydride would be formed which is an ionic compound (we don't know about it much so we can assume this option incorrect). Now, with B, hydrogen displaces the copper and forms steam (g) which is cooled to form water (the colorless liquid).
For 29, it's being done using elimination; since copper does react with AgNO3, it loses electrons to form the positive ions so A is correct. B is correct too since the mass of silver gradually increases as it is being displaced. D is also correct since Copper (II) Nitrate is blue and it will turn the solution blue as well. So, the only incorrect statement is C.

Thank you so much.

 

[Khadija_1234]

Q28. As you go down the reactivity series, the elements make less stable compounds, among these options, CuO is the compound of the least reactive metal so the answer is B.
Q29. I did this question by elimination. Cu is obviously oxidised because its oxidation state changes from 0 to 2+, as the reaction proceeds, the amount of silver displaced thus deposited will increase so A and B are right, the colour of aq. Cu2+ compounds is blue so D is right, thus C is the answer.

Thanks!

 

[usama321]

Suchal Riaz I think it is wrong in the mark scheme

 

[Amnaa]

how to convert g/dm3 into mol/dm3?

 

[usama321]

how to convert g/dm3 into mol/dm3?

Just convert the grams into moles by divding with Mr.

Lets say HCl of concentration 18.25 g/dm3
now divide 18.25 from HCl Mr. 18.25/36.5 =0.5 moles
so concentration would be 0.5 mol/dm3

 

[inquisitiveness]

what is conduction in terms of cells

 

[Buland Iqbal]

Which process is involved when translocation takes place in plants, i.e movement of glucose or sucrose from leaves to other parts of plants
Saad Mughal thementor ritx