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NEET PHYSICSEasy

A particle moves from position r1=3i^+2j^6k^\vec{r}_1= 3\hat{i}+2\hat{j}-6\hat{k} to position r2=14i^+13j^+9k^\vec{r}_2=14\hat{i}+13\hat{j}+9\hat{k} under the action of force 4i^+j^+3k^ N4\hat{i}+\hat{j}+3\hat{k} \text{ N}. The work done will be:

A

100 J100 \text{ J}

B

50 J50 \text{ J}

C

200 J200 \text{ J}

D

75 J75 \text{ J}

Step-by-Step Solution

Given, Initial position vector, r1=3i^+2j^6k^\vec{r}_1 = 3\hat{i} + 2\hat{j} - 6\hat{k} Final position vector, r2=14i^+13j^+9k^\vec{r}_2 = 14\hat{i} + 13\hat{j} + 9\hat{k} Force acting on the particle, F=4i^+j^+3k^ N\vec{F} = 4\hat{i} + \hat{j} + 3\hat{k} \text{ N}

The displacement vector d\vec{d} is given by: d=r2r1\vec{d} = \vec{r}_2 - \vec{r}_1 d=(14i^+13j^+9k^)(3i^+2j^6k^)\vec{d} = (14\hat{i} + 13\hat{j} + 9\hat{k}) - (3\hat{i} + 2\hat{j} - 6\hat{k}) d=(143)i^+(132)j^+(9+6)k^=11i^+11j^+15k^\vec{d} = (14 - 3)\hat{i} + (13 - 2)\hat{j} + (9 + 6)\hat{k} = 11\hat{i} + 11\hat{j} + 15\hat{k}

The work done WW by a constant force is the dot product of the force vector and the displacement vector : W=FdW = \vec{F} \cdot \vec{d} W=(4i^+j^+3k^)(11i^+11j^+15k^)W = (4\hat{i} + \hat{j} + 3\hat{k}) \cdot (11\hat{i} + 11\hat{j} + 15\hat{k}) W=(4×11)+(1×11)+(3×15)W = (4 \times 11) + (1 \times 11) + (3 \times 15) W=44+11+45=100 JW = 44 + 11 + 45 = 100 \text{ J}

Thus, the work done is 100 J100 \text{ J}.

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