A uniform force of (3i + j) newton acts on a particle of mass 2 kg. Hence the particle is displaced from position (2i + k) metre to position (4i + 3j - k) metre. The work done by the force on the particle is (a) 13 J (b) 15 J (c) 9 J (d) 6 J

Answer: (c). s = (4-2)i + 3j + (-1-1)k = 2i + 3j - 2k m W = F = 3(2) + 1(3) + 0(-2) = 9 J (mass is not needed) So the answer is (c) 9 J.

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Q19NEET 2013Easy

Work by a Constant Force

A uniform force of $\left(3\hat{i} + \hat{j}\right)$ newton acts on a particle of mass 2 kg. Hence the particle is displaced from position $\left(2\hat{i} + \hat{k}\right)$ metre to position $\left(4\hat{i} + 3\hat{j} - \hat{k}\right)$ metre. The work done by the force on the particle is

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Answer: (c)

$\vec{s} = (4-2)\hat{i} + 3\hat{j} + (-1-1)\hat{k} = 2\hat{i} + 3\hat{j} - 2\hat{k}$ m
$W = \vec{F}\cdot\vec{s} = 3(2) + 1(3) + 0(-2) = 9$ J (mass is not needed)
So the answer is (c) 9 J.

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