Physics: Post your doubts here!

[Shimmery woods]

I think the total kinetic energy of the girl remains constant.Because no external forces act except for the weight and the jumping action(which in turn creates an upward force greater than the weight ( so girl moves up). Therefore,
Resultant is constant.
But kinetic energy is affected by velocity which has direction.so when girl moves up the velocity becomes (+) and when she falls (-) and at the top point zero.

Hope this helps <3 <3

THANKYOU!!

 

[Mstudent]

THANKYOUUU!!

You are welcome anytime!!

 

[Shimmery woods]

que no 36 anyone..

 

[Shimmery woods]

25 and 26 please

 

[Shimmery woods]

que 19 please

 

[Shimmery woods]

que 6 aswell

 

[Shimmery woods]

que 8

 

[Shimmery woods]

que 3 ....last doubt of this paper

 

[Mstudent]

25 and 26 please

For q. 26:

equation for doppler effect:

[Speed of sound X Frequency of source]/[Speed of sound + or - speed of source]

so just put in the values and subtract when speed of sound - speed of source (approaching) from speed of sound + speed of source (Receding) ANS= C

for q. 25

for the length of wavelength: I used d = S X T

so wavelenght = 330 X 500 X 10^-6 = 0.165 m

so a translation of 0.165m means shift the graph by 1 lambda or 2 pi or 360 degrees

so basically it will be the same graph ANS= D

hope that helps

 

[janedoe]

I=A^2
Intensity for wave 1 is given which is equal to amplitude (2*10^-2)^2
Amplitude for wave 2 is (3*10^-2)^2. Find the intensity of wave 2 by cross multiplying and the answer you'll get is C.

The y-axis is labelled pressure instead of displacement; so how can we read off amplitude directly?

 

[janedoe]

Under what conditions do you suggest that the time taken is equal in both waves?

You're right. So my method is invalid. Can you please explain the correct method to obtain the answer?

 

[Thelastmoment]

You're right. So my method is invalid. Can you please explain the correct method to obtain the answer?

furuta said it so there's no need repeating the same thing

 

[nigeller]

dude i love you

 

[amina1300]

Do u want me to show you how I got the answers?
of course yes

Umm aren't u going to show working?

Q13 F1d1 + F2d2 =Ftdt
16000*0.6 +9000*2.1 =(16000+9000)*
28500÷2500=s
d=1.14m

Q10.
velocity upwards = +ve Total momentum before = 0 After = 0
100*-8 + 50 *v1sin60 + 50*v2sin60 = 0
800 = v1 sin 60 + vs sin60
(800/50)/sin60 = v1 + v2

v1 + v2 = 18.4752 (v1 and v2 have equal magnitudes)
18.4752/2 = 9.2

ans = B

Q28
Distance between the 2 sucessive wavefronts = lamda ( For both curved or straight waves)
v = f *lamda
f = 1/T c = v
c/lamda =1/T
lamda/c = T

Time when wavefront GH reaches point P;

3 lamda;
so,T = 3* lamda/c

ans = C

Hope this helps

 

[amina1300]

que 19 please

Loss in Potential Energy + work done by frictional force = Gain in Kinetic Energy
mgh + 400*250 = 0.5 *500*v^2
(500 *9.81 *100000)/250 = v^2
sqrt (ans) = 13.87

Ans = A

 

[amina1300]

O

que 3 ....last doubt of this paper

Only Ans A is correct as if wind blows, the aeroplane will move in the same direction as wind ( accelerate in that direction) and the velocity in wind will have a lower magnitude that without wind effect.

 

[amina1300]

que 8

Areas under the graph (5-0.8)*20/2 + 0.8*20

 

[Holmes]

Q13 F1d1 + F2d2 =Ftdt
16000*0.6 +9000*2.1 =(16000+9000)*
28500÷2500=s
d=1.14m

Q10.
velocity upwards = +ve Total momentum before = 0 After = 0
100*-8 + 50 *v1sin60 + 50*v2sin60 = 0
800 = v1 sin 60 + vs sin60
(800/50)/sin60 = v1 + v2

v1 + v2 = 18.4752 (v1 and v2 have equal magnitudes)
18.4752/2 = 9.2

ans = B

Q28
Distance between the 2 sucessive wavefronts = lamda ( For both curved or straight waves)
v = f *lamda
f = 1/T c = v
c/lamda =1/T
lamda/c = T

Time when wavefront GH reaches point P;

3 lamda;
so,T = 3* lamda/c

ans = C

Hope this helps

Thanks! amina1300

 

[dumbledore.]

Answer:

I guess,
K . E= 1/2 x m x v2(squared)
= 1/2 x 500 x 2 (2)
=1000 J

then,
G.p.e = mgh
re-arrange to
m= G.p.e/( g x h)
=1000J / (9.81 x 15 )
= 6.8kg


6.8kg for 100%
m1 kg for 10%
cross multiply to get 0.68kg so answer is B.

Thankyouuu

 

[Shimmery woods]

please help me with que no 35