__Question 6.11__:*z*-axis of a coordinate system is subject to a constant force

**F**given by

F = -

**i**+ 2

**j**+ 3

**k**N

Where i, j, k are unit vectors along the

*x*-,

*y*- and

*z*-axis of the system respectively. What is the work done by this force in moving the body a distance of 4 m along the

*z*-axis?

__Solution__:Force exerted on the body, F = -

**i**+ 2

**j**+ 3

**k**N

**k**m

Work done, W =

**F**.s

= (-

**i**+ 2

**j**+ 3

**k**).(4

**k**)

= 0 +0 + 3 X 4

= 12 J

Hence, 12 J of work is done by the force on the body.

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