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A cord is used to lower vertically a blo...

A cord is used to lower vertically a block of mass M through a distance d at a constant downward acceleration `(g)/(4)` Consider the following statements:
1. The block is freely falling under gravity.
2. The cord is doing work one the block.
3. The amount of work done is `((3Mgd))/(4)`

A

1 and 2 only

B

1 and 3 only

C

2 and 3 only

D

1, 2 and 3

Text Solution

Verified by Experts

The correct Answer is:
C
As the mass Mis accelerating downwards Hence, the net force,
`F=Mg-Ma=Mg-(Mg)/(4)=(3)/(4)Mg`
Thus the work done by the cord on the block in moving the distance d.
`W=F.S=(3)/(4)Mgd.`
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Knowledge Check

  • A cord is used to lower vertically a block of mass M by a distance d with constant downward acceleration (g)/(4) . Work done by the cord on the block is

    A
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    B
    `3Mg(d)/(4)`
    C
    `-3Mg(d)/(4)`
    D
    Mgd

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    A
    `(Mgd)/(4)`
    B
    `-(Mgd)/(4)`
    C
    `(3Mgd)/(4)`
    D
    `-(3Mgd)/(4)`

  • A string is used to pull a block of mass m vertically up by a distance h at a constant acceleration (g)/(3) . The work done by the tension in the string is

    A
    `(2)/(3)mgh`
    B
    `(-mgh)/(3)`
    C
    `mgh`
    D
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