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Find the initial acceleration of block B

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  1. Dec 6, 2017 #1
    1. The problem statement, all variables and given/known data
    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.

    2. Relevant equations
    3. The attempt at a solution

    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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  3. Dec 6, 2017 #2

    PeroK

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    Try drawing a diagram of the situation after a short time. Hint: where are the two blocks?
     
  4. Dec 6, 2017 #3
    Please see the attachment.
     
  5. Dec 6, 2017 #4

    PeroK

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    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.
     
  6. Dec 6, 2017 #5
    The acceleration is zero since there are no forces.
     
  7. Dec 6, 2017 #6

    PeroK

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    Are you sure? That means the block won't move?
     
  8. Dec 6, 2017 #7
    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?
     
  9. Dec 6, 2017 #8

    PeroK

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    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.
     
  10. Dec 6, 2017 #9
    May be
     
  11. Dec 6, 2017 #10

    haruspex

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    Agreed. Should more than double that.
    Or just instantaneously at rest, the two blocks having previously been propelled leftwards and upwards respectively.
     
  12. Dec 6, 2017 #11

    PeroK

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    Slightly trickier for a lab technician to arrange!
     
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