Physics: Post your doubts here!

[saturn21]

Someone plzz help me on this thanks in advance
Q9 and Q10... I didnt get it :/
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This is a repeat qstn but i still didnt get it :/
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Any quick way to calculate the energy except for counting boxes... Its time consuming...
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I didnt get it.... Why isnt it C? I mean the gradient of I/V should be highest so that V/I should be lowest and R=V/I so R should be lowest...
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[DaniyalK]

Why is C wrong??View attachment 54903( ans is A)

Force needs to be perpendicular to the pivot for maximum pivot. Draw a straight line from the center of the handle to the tip. F needs to be perpendicular to this line.

 

[DaniyalK]

View attachment 54914

Initial KE: 0.5*m*v^2 = 0.5mv^2
Initial momentum = final momentum
mv = 2m(final velocity)
final velocity = v/2
Final KE: 0.5 * 2m * (v/2)* = 0.25mv^2

 

[saturn21]

Anyone?? Answer is A

 

[Ahmed Aqdam]

Isn't mm into m, 500 x 10^-3?

There are 500 lines in every mm. There are 1000 mm in every meter so 500*1000.
If you take the d first in mm by 1/500=2*10^-3 then this will be multiplied by 1*10^-3.

 

[princess Anu]

Force needs to be perpendicular to the pivot for maximum pivot. Draw a straight line from the center of the handle to the tip. F needs to be perpendicular to this line.

do u mean like this?? but pivot is the thing to which handle is attached, no? :

 

[Studydayandnight]

HELPPPPPP.

Correct answer is C.

 

[Studydayandnight]

Which process doesn't require energy to be supplied?

A. Boiling
B.Evaporation
C.Freezing
D.melting

Isn't the correct answer Evaporation??

The mark scheme says C. :/

 

[DaniyalK]

do u mean like this?? but pivot is the thing to which handle is attached, no? :

Your arrow doesn't start at the pivot. Look at A and C, F is at an angle to the line from the pivot in C but it is closer to 90 degrees in A, so there will be a larger moment in A.

 

[nehaoscar]

Wire is of same steel so same Young Modulus. The difference will be in extension.

Compression is proportional to length but also inversely proportional to area of cube.

But then the option says delta l is proportional to L (being the length and not the area l^2)??

 

[DaniyalK]

HELPPPPPP.

Correct answer is C.

mgh = 0.5mu^2
u = sqrt(2gh)
mg(h/2) = 0.5mv^2
v = sqrt(gh)

Which process doesn't require energy to be supplied?

A. Boiling
B.Evaporation
C.Freezing
D.melting

Isn't the correct answer Evaporation??

The mark scheme says C. :/

boiling, melting and evaporation all involve breaking bonds, which is endothermic.

 

[nehaoscar]

Ok so in this case they've just added the actual uncertainties to get D
But then when would you use the percentage uncertainty to get the value? (which gives A here)
Why don't you use % uncertainty in this question??

 

[Ahmed Aqdam]

But then the option says delta l is proportional to L (being the length and not the area l^2)??

The area is l^2 so compression is inversely proportional to l^2 and directly to l.

 

[Ahmed Aqdam]

View attachment 54922
Ok so in this case they've just added the actual uncertainties to get D
But then when would you use the percentage uncertainty to get the value? (which gives A here)
Why don't you use % uncertainty in this question??

The two quantities are being subtracted and not multiplied or divided.

 

[nehaoscar]

The area is l^2 so compression is inversely proportional to l^2 and directly to l.

But then the answer says compression (delta l) is inversely proportional to l (option B is the answer)
Then it should be A or C right??

 

[nehaoscar]

The two quantities are being subtracted and not multiplied or divided.

So when its addition and subtraction, simply add up the actual uncertainty
and when it's multiplication or division, then use % uncertainty correct?

 

[Ahmed Aqdam]

But then the answer says compression (delta l) is inversely proportional to l (option B is the answer)
Then it should be A or C right??

It is directly proportional to l and also inversely proportional to l^2.
So in overall equation it is proportional to l/l^2. Simplify to get 1/l.

 

[Ahmed Aqdam]

So when its addition and subtraction, simply add up the actual uncertainty
and when it's multiplication or division, then use % uncertainty correct?

Yes.

 

[nehaoscar]

It is directly proportional to l and also inversely proportional to l^2.
So in overall equation it is proportional to l/l^2. Simplify to get 1/l.

Oh ok! Thankyou!

 

[princess Anu]

Yes.

Do we always quote uncertainty to 1 sig fig or it depends on the values given?