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+1 vote
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in Work, Energy and Power by (20 points)
A force F=4(xy²+yx² j) acts on a particle, moving along parabolic path. The work done by this force in moving the particle from (1, 1) to (2, 4) is (where F is in newton and x, y are in meter)

 (1) 100 J

 (2) 120 J

 (3) 136 J

 (4) 126

answer is 4 

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1 Answer

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by (50.1k points)

Correct option is (4) 126 J

\(w = \int dw . \int f.ds\)

\(w = 2\int\limits_{(1, 1)}^{(2, 4)} (xy^2 \hat i + yx^2 \hat j).(dx\hat i + dy\hat j)\)

\(= 2 \left[\frac{x^2y^2}{2} + \frac{y^2 x^2}2 \right]_{(1, 1)}^{(2, 4)}\)

\(= 2 \left[x^2 y^2\right]_{(1,1)}^{(2, 4)}\)

\(= 2[4 \times 16] - 2[1]\)

\(= 2 (64 - 1)\)

\(= 2 \times 63\)

\(= 126\ J\)

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