Physics: Post your doubts here!

[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?

 

[princess Anu]

What exactly is wrong in option B?

 

[princess Anu]

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.

help...ans is B ..

 

[DaniyalK]

Someone plzz help me on this thanks in advance
Q9 and Q10... I didnt get it :/
View attachment 54905
This is a repeat qstn but i still didnt get it :/
View attachment 54906
Any quick way to calculate the energy except for counting boxes... Its time consuming...
View attachment 54907
View attachment 54909
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...
View attachment 54910
View attachment 54911

9: initial momentum = final momentum
m(2v) + 3m(-v) = 4m(vf)
vf = -v/4
10: Just move the arrows around in your head without changing their direction to make a triangle. D is the only way you can make the triangle with the arrows in their original direction.
12: Take the pivot at the point where the ladder meets the wall. All distances must be perpendicular to the forces. F is perpendicular to h and W is perpendicular to a/2a. Equate the clockwise and anticlockwise moments.
21: Just draw a triangle with base .3 m and height 17 N. Area under the triangle is 2.6 but obviously the graph has less area than this so A is the only possible option.
30: Before the switch is opened, 2 and 3 are in parallel, so their resistance is less and their pd is less, while 1's pd is high. when the switch is opened, it becomes a series circuit, so the pd of 2 increases and 1's share of the pd decreases ( think of it as a potential divider circuit)
34: Smallest resistance is at the point where the ratio of V to I is least.
38: Speed of alpha particle is about 5% of the speed of light

 

[princess Anu]

How can we estimate volume of an adult head?
any tip for the estimations please?

 

[Ahmed Aqdam]

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

Uncertainty in a measured quantity is always to 1 significant figure.

 

[princess Anu]

ans is c help