1.

If the constant forces `2hati-5hatj+6hatk and -hati+2hatj-hatk` act on a particle due to which it is displaced from a point A (4,-3,-2) to a point B (6,1,-3), then the work done by the forces isA. 10 unitsB. `-10` unitsC. `-15` unitsD. `-9` units

Answer» Correct Answer - A
Resultant force,
`F=(2hati-5hatj+6hatk)+(-hati+2hatj-hatk)=hati-3hatj+5hatk` and displacement
`d=(6hati+hatj-3hatk)-(4hati-3hatj-2hatk)=2hati+4hatj-hatk`
`:." "` Work done W `= F* d=( hati-3hatj+5hatk)*(2hati+4hatj-hatk)=-15`
`=-15` units [ neglecting - ve sign]


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