@JohnRennie are you free for some time sir?

@harambe I'm here for a few hours

@JohnRennie cool..I will ping you when I am free

@JohnRennie sir are you there?

@harambe OK

@Akash.B hi, yes, I'm around

I encountered a problem while reading quantum mechanics

@JohnRennie is higgs field and higgs boson are same?

@Akash.B no

The Higgs boson is an excitation of the Higgs field.

so you mean both are different

My phone's ringing. I'll be a few minutes ...

okay

@Akash.B the Higgs field is a quantum field and it's a complicated object. In particular there are several ways it can interact with its surroundings i.e. exchange energy with its surroundings.

One of those ways is by creating or annihilating Higgs bosons.

So the Higgs boson is a particle associated with the Higgs field, but the two are not the same thing.

oh

@JohnRennie imgur.com/RdZiogW

Shouldn't net force be zero

On the phone ...

I'm not sure I understand the question ...

For a start, is the lift accelerating upwards or downwards?

Its not given so I assume we take cases ......

One will be in a planet with g+a and another with g-a like you said

Well suppose it's accelerating downwards. In that case the effective gravity in the lift is $g-a$ = about 6m/s^2.

If we use F=ma we get the force on the 8kg mass = 8 x 6 = 48N, which does match one of the answers.

But I'm not sure if that's what the question means.

Well in the lift frame ,isn't the acceleration zero

I mean lift will see it stationary

The answer is 32 N

I don't understand what they are asking or where they got the answer 32N. Basically it's a rubbish question.

Okay

Hmm, I suppose if the acceleration of the lift is 4m/s^2 then since the 8kg mass is stationary relative to the lift it must also be accelerating at 4m/s^2, and 4 x 8 = 32N ...

Didn't get this

If 8 kg mass is stationary w.r.t lift then net acceleration has to be zero.Only in ground frame will it be seem with acceleration 4 m/s2

@JohnRennie imgur.com/9slxaJW

Can you tell me how to resolve F in Q11

@JohnRennie Basically in ground frame,the floor of the elevator moves with 4m/s2 so does 8 kg block that's why force comes 32N. Right?

@harambe I think this is what the question is getting at:

The block lifts off the floor when $F_v = mg$

And $F_v = F\sin\theta$

But again this is a poor question.

What would actually happen is that the block would pivot about its trailing edge no simply lift upwards.

I just realized this......I got this on my first trial but I saw the wrong answer key lol

So here the block will lift upwards as well as accelerate in horizontal direction,right?

Yes

Would it like topple over?

It would do this i.e. rotate around the trailing edge.

You'd calculate the force at which it started rotating by taking moments.

Oh

Got it

But the question obviously doesn't mean that. These are rubbish questions.

In Q12 I got tension to be 9 N at the end point .....how should I calculate from here

@harambe What is the acceleration of the block and rope?

It's stationary then only this question can be solved

At least I think.....I just equated the forces

Is the answer (A)?

On spot

Yes

OK, you're supposed to assume it's a frictionless floor so the block and rope slide along the floor. (Another rubbish question)

Okay

So what's the acceleration of the block and rope?

Wait a minute.....isn't the rope tied to a fixed point

6m\s2 of block and hopefully rope

Sorry 4 m/s2

The question doesn't say the rope is tied to anything, and if it were tied you'd get the wrong answer.

@harambe the force is 9N, the block weighs 2kg and the rope weighs 1kg, so the total weight is 3kg ...

Dn..my calculation sucks

I got it....9N/3=3m/s2

Took sin37=4/5 again

OK, now just consider the rope. What is the force being exerted at the end of the rope where the rope is tied to the block?

3N

And we may take a segment of rope now,right

Yes. If you take the right half of the rope then it weighs 0.5kg.

Because whatever holds for a complete rope holds for the segment too

@harambe well any segment of the rope is also accelerating at 3m/s^2

Tension is minimum at the end point then

If I do further analysis

All you have to do is imagine the rope as being two ropes tied together.

The force at the end of the two combined is equal to ma i.e. 3N.

The force on the rightmost "half rope" is also equal to ma, but now the mass of the half rope is only 0.5 kg.

And that gives me 1.5

Okay got this...I will be trying a constraint motion so will it be alright if I ask you where I am having doubt ?

I need to go soon, but I'll be around later

Can you give me the time frame in which you will be active again

@JohnRennie sir are you there?

@Akash.B Hi

Sir once we talked about interaction between photons and electrons

You told me that the interaction is weak

But what happens if interaction is made strong ?

@JohnRennie ^^

Does electrons loose it's complete mass?

@JohnRennie sir are you there?

Are you thinking of light passing through a transparent medium like glass?

If so then yes the interaction of the light with the electrons in the glass is quite weak

Yes sir I know it ,I want know what would happen if the interaction was made strong

@JohnRennie^^

You get strong interactions in systems like Bose-Einstein condensates, and you can get some very odd effects. For example it's possible to slow the speed of light almost to a stop.

See for example this web site

Or this site

@JohnRennie will you be usually active by 6 pm ?

@Koolman I think there is a typo on the question you posted at MathSE.i have added an answer