Physics: Post your doubts here!

[h4rriet]

Q1 A box of mass 8.0 kg rests on a horizontal, rough surface. A string attached to the box passes
over a smooth pulley and supports a 2.0 kg mass at its other end.
When the box is released, a friction force of 6.0 N acts on it.
What is the acceleration of the box?
answer is 1.4ms-2
can u solve it via newton second law plz?

Q2--

An electric power cable consists of six copper wires c surrounding a steel core s
1.0 km of one of the copper wires has a resistance of 10 Ω and 1.0 km of the steel core has a
resistance of 100 Ω.
What is the approximate resistance of a 1.0 km length of the power cable?
B 1.6 Ω

1. Draw a free-body diagram on the 8 kg mass. The force to the right will be the weight of the 2 kg mass. The force backwards will be 6 N. a=F/m, and m=8+2 kg.

 

[h4rriet]

so it shd be the input power?

No, the generator is supplying this power because of the power generated by the water.

 

[Aries_95]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_12.pdf
Q.17 and 31 anyone?

 

[TaffsAsLevel]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_12.pdf
Q.17 and 31 anyone?

For 17. click attachment

for 31. Its B because it is a positive charge repel means it goes opposite to arrow for repel and it says X to Y, but also increasing force which means lines become concentrated rather than uniform lines. Hope you get it

 

[falcon678]

people can anyone please explain how calculate uncertainties in wich the values are dividing multiplying and the percentage uncertainty....?
thanks!

 

[Aries_95]

For 17. click attachment

for 31. Its B because it is a positive charge repel means it goes opposite to arrow for repel and it says X to Y, but also increasing force which means lines become concentrated rather than uniform lines. Hope you get it

Thank you

 

[msaad@121]

can someone explain question 26 of 9709/11/o/n/2009 please

 

[Aries_95]

can someone explain question 26 of 9709/11/o/n/2009 please

d=10^3/300=3.33m.
d sin θ=nλ
3.33 sin 90= (n/2)x (450x10^-9)
n=14.8=15 hence D.

 

[Kyusam]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w11_qp_11.pdf
Need help in Q.30 and In Q. 32 I don't get why it's anti-clockwise b'coz since -ve charge repel it will move in clockwise so is it anti-clockwise to make it stable or what ??? do help please !!

 

[Rahma Abdelrahman]

No, the generator is supplying this power because of the power generated by the water.

Oh.. got it! Thanks

 

[white rose]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_w11_qp_12.pdf
can anyone explain me q. 15, 16 & 26...ur help is highly appreciated..

 

[sara kamal]

Can you help me out then on June 2010 paper 11 question 33

here u have to assume a value of p.d=eg:6 V
so current in circuit =power/voltage=2 amp
nw voltage across P would be 4V and across Q and R would be 2V since they are in parallel
see hw itS 2V(ASSUMING EACH RESISTANCE TO BE 3,SO TOTAL R OF RESISTORS IN PARALLEL=1.5 OHM
NW THERE SHARE OFBATTERYS VOLTAGE=1.5/4.5(TOTAL R) x 6=2V)
anyway nw,
nw since P=VI
power in P=2 x 1(since divided between Q and R=2W

hope u got it,i tried my best

 

[sma786]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s11_qp_11.pdf
Can i know how to get the answer for question 5? its 'A' bdw ..

 

[Tanvir Azad]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_11.pdf
Can i know how to get the answer for question 5? its 'A' bdw ..

In question no. 5, fractional uncertainty is being asked.... so:
as speed = distance traveled / time taken
here, distance traveled is 385 - 115 = 270, and its uncertainty is, 1+1= 2mm (its not 1mm bcoz we have to take the uncertainties of both the initial and final values of distance travelled)
again for time taken, 3.5 - 1.5 = 2.0 and its uncertainty is .02 + .02 =0.04mm (same reason as above)
hence, there fractional uncertainties should be, 2/270 + 0.04/2.00
So the key is A.

Hope it helped...

 

[sma786]

In question no. 5, fractional uncertainty is being asked.... so:
as speed = distance traveled / time taken
here, distance traveled is 385 - 115 = 270, and its uncertainty is, 1+1= 2mm (its not 1mm bcoz we have to take the uncertainties of both the initial and final values of distance travelled)
again for time taken, 3.5 - 1.5 = 2.0 and its uncertainty is .02 + .02 =0.04mm (same reason as above)
hence, there fractional uncertainties should be, 2/270 + 0.04/2.00
So the key is A.

Hope it helped...

Thankyou very very much

 

[sma786]

http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s11_qp_11.pdf
question 10 anybody? why is the answer -2mu? why not -mu?

 

[Tkp]

gary221
26
the ans is b

 

[TaffsAsLevel]

here u have to assume a value of p.d=eg:6 V
so current in circuit =power/voltage=2 amp
nw voltage across P would be 4V and across Q and R would be 2V since they are in parallel
see hw itS 2V(ASSUMING EACH RESISTANCE TO BE 3,SO TOTAL R OF RESISTORS IN PARALLEL=1.5 OHM
NW THERE SHARE OFBATTERYS VOLTAGE=1.5/4.5(TOTAL R) x 6=2V)
anyway nw,
nw since P=VI
power in P=2 x 1(since divided between Q and R=2W

hope u got it,i tried my best

It's ok I found it out already, thank you for the effort just ask me if you have doubt

 

[TaffsAsLevel]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s11_qp_11.pdf
Can i know how to get the answer for question 5? its 'A' bdw ..

Add the percentage uncertainties, you want deltav/v, and if you still have problem to find out the uncertainty in s and t, remember that if we're given difference we always ADD the uncertainties

 

[Tkp]

gary221

help me in q 14
ans is b