Find the initial acceleration of block B

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SUMMARY

The initial acceleration of block B, connected to a 1 kg mass by a non-stretchable string, is determined to be 2g, contrary to initial assumptions of g. The negligible mass of block B implies zero tension in the string, leading to confusion regarding the forces acting on the system. A diagram illustrating the system's dynamics after the particle moves is essential for understanding the forces at play. The discussion emphasizes the importance of considering external forces to maintain the 1 kg block in place during the experiment.

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  • Understanding of Newton's laws of motion
  • Familiarity with concepts of tension in strings
  • Knowledge of basic kinematics
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Vivek098
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Homework Statement


a block B of negligible mass is connected to a particle of mass 1 kg with a non-stretchable string. Now the hanging particle is given a velocity root(8gH) horizontally when system is at rest. Find the initial acceleration of block B.

Homework Equations


3. The Attempt at a Solution [/B]
Since Mass of Block is negligible, so Tension in String is Zero. Now for Block A, only force acting is mg in downward direction. So, acceleration of Block A is g in downward direction always. In the initial state, the acceleration of block A is equal to acceleration to Block B since they are directly connected by string. So, acceleration of Block B should be g towards right. But actual answer given is 2g.
 

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Vivek098 said:

Homework Statement


a block B of negligible mass is connected to a particle of mass 1 kg with a non-stretchable string. Now the hanging particle is given a velocity root(8gH) horizontally when system is at rest. Find the initial acceleration of block B.

Homework Equations


3. The Attempt at a Solution [/B]
Since Mass of Block is negligible, so Tension in String is Zero. Now for Block A, only force acting is mg in downward direction. So, acceleration of Block A is g in downward direction always. In the initial state, the acceleration of block A is equal to acceleration to Block B since they are directly connected by string. So, acceleration of Block B should be g towards right. But actual answer given is 2g.

Try drawing a diagram of the situation after a short time. Hint: where are the two blocks?
 
Please see the attachment.
 
Vivek098 said:
Please see the attachment.

You need a diagram after the particle has moved somewhat!

Hint: assume the experiment is taking place on the horizontal. I.e. ignore the vertical force of gravity. What do you get then?

PS The answer of ##2g## looks wrong to me.
 
PeroK said:
You need a diagram after the particle has moved somewhat!

Hint: assume the experiment is taking place on the horizontal. I.e. ignore the vertical force of gravity. What do you get then?

PS The answer of ##2g## looks wrong to me.
The acceleration is zero since there are no forces.
 
Vivek098 said:
The acceleration is zero since there are no forces.

Are you sure? That means the block won't move?
 
PeroK said:
Are you sure? That means the block won't move?
How could be system initially at rest as mentioned in question. How block b will hold the tension produce in string by 1 kg block?
 
Abhishek kumar said:
How could be system initially at rest as mentioned in question. How block b will hold the tension produce in string by 1 kg block?

The 1kg block must be held in place by some external force: it perhaps ought to have been shown at the edge of a small supporting platform.
 
PeroK said:
The 1kg block must be held in place by some external force: it perhaps ought to have been shown at the edge of a small supporting platform.
May be
 
  • #10
PeroK said:
The answer of 2g looks wrong to me.
Agreed. Should more than double that.
PeroK said:
The 1kg block must be held in place by some external force
Or just instantaneously at rest, the two blocks having previously been propelled leftwards and upwards respectively.
 
  • #11
haruspex said:
Or just instantaneously at rest, the two blocks having previously been propelled leftwards and upwards respectively.

Slightly trickier for a lab technician to arrange!
 

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