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An object is displaced from point $A(2m,3m,4m)$ to a point B $(1m, 2m, 3m) $ under a constant force. $\hat F=(2 \hat i+3 \hat j+4 \hat k)$. Find the work done by the force

\[(a)\;-9\;J \quad (b)\;6 \;J \quad (c)\; 9 \;J \quad (d)\;-6\;J\]

1 Answer

$W=\hat F.\hat {ds}$
$\hat {ds}=\hat r_f-\hat r_i$
$\hat {ds}=(\hat i+2 \hat j+3 \hat k)-(2 \hat i+3 \hat j+4 \hat k)$
$\quad=(-\hat i-\hat j-\hat k)$
$W=(2 \hat i+3 \hat j+4 \hat k).(-\hat i - \hat j -\hat k)$
$\quad= -9 J$
Hence a is the correct answer. 


answered Aug 7, 2013 by meena.p
edited Feb 17, 2014 by meena.p

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