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# A particle moves with velocity $v= (5 \hat i -3 \hat j+6 \hat k) m/s$ under the influence of a constant force $\hat F=(10 \hat i+10 \hat j+20 \hat k)N$. The instantaneous power applied to the particle is

$(a)\;200\;J/s \quad (b)\;140\;J/s \quad (c)\; 40\;J/s \quad (d)\;170 J/s$

$P=\hat F.\hat V$
$\quad=(5 \hat i-3 \hat j+6 \hat k).(10 \hat i+10 \hat j+20 \hat k)$
$\quad=50-30+120$
$\quad=140\;J/s$
Hence b is the correct answer
edited Jun 11, 2014