Question

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Answer 1

Answer:

In the string elastic force is conservative in nature.

∴W=−△U

Work done by elastic force of string.

W=−(U

F

−U

i

)=U

i

−U

F

W=

2

1

kx

2

−

2

k

(x+y)

2

=

2

1

kx

2

−

2

1

k(x

2

+y

2

+2xy)

=

2

1

kx

2

−

2

1

ky

2

−

2

1

kx

2

−

2

1

k(2xy)

=−kxy−

2

1

ky

2

Therefore, the work done against elastic force

W

external

=−W=

2

ky

(2x+y).