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5.Work, Energy, Power and Collision
normal
A force of $\left( {2\hat i + 3\hat j + 4\hat k} \right)\,N$ acts on a body for $4\, sec$ and produces a displacement of $\left( {3\hat i + 4\hat j + 5\hat k} \right)\,m.$ The power used is ............. $\mathrm{W}$
A
$4.5$
B
$6.5$
C
$7.5$
D
$9.5$
Solution
$P=\frac{\overrightarrow{\mathrm{F}} \cdot \overrightarrow{\mathrm{S}}}{t}=\frac{(2 \hat{\mathrm{i}}+3 \hat{\mathrm{j}}+4 \hat{\mathrm{k}}) \cdot(3 \hat{\mathrm{i}}+4 \hat{\mathrm{j}}+5 \hat{\mathrm{k}})}{4}$
$=\frac{6+12+20}{4}=9.5 \mathrm{Watt}$
Standard 11
Physics
