Physics: Post your doubts here!

[Minsa Fatima]

8

3.5 in top half 3.5 in bottom half = 7 + 1 central = 8

Shouldnt that be in whole numbers? 2*3 +1=7

 

[amina1300]

LOL I chose D. I hope it's correct. It would be if:

1. Zaki doesn't remember right and W was just the weight as in the 2015 question
2. Option D said 'force on Earth from book"

Oh that was D I chose the option with the force of table on book, whatever option that was There is some exam paper of before 2013 with that same question I remember it now as I got it in my school exam paper 2 times and I always used to do it wrong by choosing what you chose. Im still confused as to whether Im correct now or not!

 

[Zaki ali asghar]

What about the graph question which was a friction less slope?

 

[amina1300]

8

3.5 in top half 3.5 in bottom half = 7 + 1 central = 8

I guess I wrote 6 in this one hmm... didn't know how to solve it. but what I do know that 3.5 becomes 3 +3 +1 ---> 7.

 

[Metallic9896]

No thats not how its done,the ans was 3.5.You dont round up to nearest integer for maxima,3 at the top 3 at bottom and one central so total of 7.

Ah darn it I know I know idk what I did lol I did a similar question that bothered my friends yesterday without any problem dunno what happened in the paper. Lol

 

[Metallic9896]

I guess I wrote 6 in this one hmm... didn't know how to solve it. but what I do know that 3.5 becomes 3 +3 +1 ---> 7.

3.5 means 3 whole maximas. The 0.5 won't count. But that 3 whole means on 90 degrees in top half. So you x2 = 6 total maximas at angles, and 1 central at 0 angle which you have to count anyway so 7.

 

[Metallic9896]

What about the graph question which was a friction less slope?

It was A vs. C and then A cause C implied a greater final velocity than initial but that's impossible since no input from any force and mgh was the same as it came back to same height as it initially had, so had to be A.

 

[Zaki ali asghar]

I did A at first too but if you had looked closely the point S was at lower level than the original point from where it started so the loss in pe was converted to Kinetic energy hence the greater speed.

 

[Metallic9896]

I did A at first too but if you had looked closely the point S was at lower level than the original point from where it started so the loss in pe was converted to Kinetic energy hence the greater speed.

If you're absolutely sure then you're right.

 

[amina1300]

"That q about sqrtmgh was C, the sum of m sqrt 2gh1 and m sqrt 2gh2"
and "the The one about air resistance was C, the scary looking equations. I got it wrong"

How can they be C?

 

[amina1300]

What about the phase difference question?

 

[amina1300]

The question with the 10 revolutions per second and we had to find wavelength of wave ??

 

[Metallic9896]

"That q about sqrtmgh was C, the sum of m sqrt 2gh1 and m sqrt 2gh2"
and "the The one about air resistance was C, the scary looking equations. I got it wrong"

How can it be C both of them?

These were two separate questions or at least I'm referring to separate ones in my answer above lol. The first one was the object falling height h1 then bouncing back up to h2 so what was change in momentum.

Change in momemtum is final momemtum - initial momemtum, but since the velocities will be in opposite direction, if you take downwards as negative and upwards as positive, final - initial = m(v2 - (-v1)) = m(v2 + v1)

So only C was giving that and you get v by the sqrt 2gh by 2as = v squared - u squared and assuming u squared to be zero in initial and v squared to be zero in final

As for the air resistance one I don't remember the explanation but my friend explained it clearly and it was C

 

[Metallic9896]

The question with the 10 revolutions per second and we had to find wavelength of wave ??

10 revolutions in 1 second
50 teeth in 1 revolution
1 teeth = 1 Hz for that metal strip thing
50 x 1 = 50 Hz in one revolution if one revolution per second
10 x 50 = 500 Hz in ten revolutions if ten revolutions per second

v = f x wavelength
330 was v
330/500 = 0.66m

 

[Metallic9896]

What about the phase difference question?

I did lambda/4 for the one in which phase difference was 90 degrees and we had to find potential wavelength difference

I did 180 degrees and 'same' amplitude, they'd be oscillating with opposite displacements but since amplitude is a scalar quantity it would be the same, for the question prior to that in which they asked about two antinodes or any other points that are half a wavelength apart (excluding nodes of course)

 

[amina1300]

Yay these 3 questions are correct!

 

[Metallic9896]

Yay these 3 questions are correct!

haha yayy!

 

[shahzaib ihsan]

only people in this forum wronged my 5 questions! i don't know how many more..

I did A at first too but if you had looked closely the point S was at lower level than the original point from where it started so the loss in pe was converted to Kinetic energy hence the greater speed.

i am absolutely sure that the second slope ( the one in which the ball fall) was more steep in the picture, as well as the graph of 2nd slope was steeper than first ones

 

[amina1300]

What was the load unload graphs answer?

 

[shahzaib ihsan]

What was the load unload graphs answer?

what did you choose