Calculating Tension in Friction & Pulley: Solving for a=3 m/s^2

[gracy]

As tension force never pushes it always pulls .So block should move forward.

 

[gracy]

Is there any tension force in the end which is tied to wall (I have pointed out that end in my below diagram)

I think there should be.

 

[haruspex]

As tension force never pushes it always pulls block should move forward.

In particular, forward relative to the car. So friction acts the other way, agreed? What, then, is the sum of forces?

 

[haruspex]

Is there any tension force in the end which is tied to wall (I have pointed out that end in my below diagram)

View attachment 81877
I think there should be.

Yes. What is the relationship between the tension there and the tension at the end attached to the block?

 

[gracy]

They should be same.As string and pulley is massless(assumption)

 

[gracy]

Wait,I think I am getting the solution now.

 

[haruspex]

They should be same.As string and pulley is massless(assumption)

Right.

 

[gracy]

I wish Mass of flat car was given!

 

[haruspex]

I wish Mass of flat car was given!

As I posted previously, you don't care about the mass of the car or the forces on it because you know exactly how it is moving. Concentrate on the forces on the block and its acceleration.

 

[gracy]

Is it correct.

 

[haruspex]

Is it correct.
View attachment 81878

Whether or not it is correct, it is irrelevant. Please just answer my questions in post ##34.

 

[gracy]

- which way does that friction force act

Backward.

- are there any other horizontal forces on the block other than friction and the string tension?

No.

what is the sum of horizontal forces on the block?

T-150N =30Kg multiplied by acceleration of the block.

what is the acceleration of the block?

Here I am struggling.

 

[haruspex]

Backward.

No.

T-150N =30Kg multiplied by acceleration of the block.

Here I am struggling.

Ok so far.
The string is of constant length. If the car moves 1m, the top part of the string gets how much longer? What does that tell you about the length of the lower part? How far has the block moved?

 

[gracy]

Sorry,actually I am really pedantic.

the top part of the string

Did you mean the part of string indicated?

 

[haruspex]

Sorry,actually I am really pedantic.Did you mean the part of string indicated?

Yes.

 

[gracy]

I think the top part of the string should be

 

[haruspex]

I think the top part of the string should beView attachment 81886

That cannot be string, or the pulley would fall down. Must be a rod.
The upper part of the string runs drom the wall to the pulley. How much longer does that get when the car advances 1m?

 

[gracy]

How much longer does that get when the car advances 1m?

Same as distance covered by small block.

 

[haruspex]

Same as distance covered by small block.

No. Forget the block for the moment, and concentrate on the car, the pulley, the wall, and the length of string from wall to pulley. If the car moves 1m further from the pulley, how much longer is that part of the string?

 

[gracy]

How much longer does that get when the car advances 1m?

Total length of string - length of the top part of the string ?

 

[haruspex]

Total length of string - length of the top part of the string ?

No, I'm asking about that top part of the string, the part that runs horizontally from the wall to the pulley.

 

[gracy]

Total length of string -(minus) length of the top part of the string .Right?/QUOTE]

 

[gracy]

Thank you for your patience .

 

[haruspex]

If the car moves 1m further from the wall, how much further is the pulley from the wall? So how much longer is the piece of string from the wall to the pulley?

 

[gracy]

1 meter?

 

[haruspex]

1 meter?

Right. So what would be the change in length of the lower part of the string, the part that runs from the block to the pulley?

 

[gracy]

So what would be the change in length of the lower part of the string

1 meter .

 

[haruspex]

1 meter .

Longer or shorter?

 

[gracy]

Longer or shorter?

Shorter?

 

[haruspex]

Shorter?

Right. So how much closer is the block to the pulley?

 

[gracy]

So how much closer is the block to the pulley?

1 meter.so distance covered by block is 1 meter,right?

 

[haruspex]

1 meter.so distance covered by block is 1 meter,right?

It is one metre closer to the pulley. But the pulley has moved how far?

 

[gracy]

But the pulley has moved how far?

1 meter?

 

[haruspex]

1 meter?

Right. So the pulley is one metre further from the wall, and the block is one metre closer to the pulley. So how far has the block moved away from the wall?

 

[gracy]

So how far has the block moved away from the wall?

1 meter.