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Physics: Post your doubts here!

Saad the Paki

Saad the Paki

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i_try9621 said:
View attachment 60723 Ans is D from 11/M/J/12
Click to expand...
This is a simple moments question.

Clockwise and anticlockwise moments must be equal for equilibrium. So if distance y is increased, we have to move the pivot to the right so that to cancel out the increase in y.
The pivot here is R . So moving Pivot to the right decreases y and increases x thus reaching an equilibrium.
 
qwertypoiu

qwertypoiu

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i_try9621 said:
View attachment 60723 Ans is D from 11/M/J/12
Click to expand...
The force L was moved to the right.
Remember that, for any system to be in equilibrium, two conditions must be satisfied:
1. No net force
2. No net moments

This second condition is violated here by moving the L to the right. But maybe you're wondering, which point should I take as the pivot when I wanna see if there is any net moments or not? The answer is ALL points must have no net moments in order for a system to be in equilibrium. But we can't check all so we usually just choose any and usually the simplest is the center.
So let's take the center.

Before, R was right at the center and so contributed no moment to this central point since its perpendicular distance to it was zero.
And L provided the clockwise moment to this center point, and W countered this with equal but anticlockwise moment.

After L is moved, we are told the system remains in equilibrium. Note that, the actual magnitude of R cannot change. This is in order to preserve the first condition (up = down)
Also, no horizontal forces can act. This again will violate the first condition (left = right)

Keeping the support (the center) as our pivot point, we see that now there is extra clockwise moment caused by L. If R moves to the left, it causes even more clockwise moment. Since we need to counter the extra moment caused by L, R must move to the right. By moving to the right, the perpendicular distance from the pivot of R is no longer zero. It causes a moment in anticlockwise direction because it acts upwards, and thus counters L (along with the help of W)

Alternatively, we can check moments upon another point, the point where force R has started acting on after moving to right. This allows ignoring the effect of R and rather looking at the effects of distance of W and L from the pivot.
 
B

Benny Wu

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Did anyone here take 2016 May/June paper 13? I would like to know the answer to the questions relating to vector, diffraction and interference.
Or does anyone have this years question papers? THX
 
Rizwan Javed

Rizwan Javed

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I solved the questions, but not sure my answers are right or wrong :p so can you please post the answers as XPFMember said :p
 
H

Hassan (SHT)

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Here are the Answers Q15 B
Q2 B
Q10 C
Q6 C
These Questions are smart enough, haha
I got the same answer for Q6 , I Wonder how gora tricks us
 
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