Jambmaths question:
U is inversely proportional to the cube of V and U = 81 when V = 2. Find U when V=3
Option A:
24
Option B:
27
Option C:
32
Option D:
36
Jamb Maths Solution:
$\begin{align} & U\propto \frac{1}{{{V}^{3}}} \\ & U=\frac{K}{{{V}^{3}}} \\ & \text{When }V=2,\text{ }U=81 \\ & 81=\frac{K}{{{2}^{3}}} \\ & K=81\times 8=648 \\ & \text{When }V=3,\text{ }U=? \\ & U=\frac{648}{{{3}^{3}}}=\frac{648}{27}=24 \\\end{align}$
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