Question

A rectangular block of size $10cm\times 8cm\times 5cm$ is kept in three different positions $P,Q$ and $R$ in turn as shown in the figure. In each case, the shaded area is rigidly fixed and a definite force $F$ is applied tangentially to the opposite face to deform the block. The displacement of the upper face will be

• A. Same in all the three cases
• B. Maximum in P position
• C. Maximum in Q position
• D. Maximum in R position

Answer 1

Answer: (D)

$\eta =\frac{F/A}{x/L}$
$\Rightarrow x=\frac{L}{\eta }\times \frac{F}{A}$
If $\eta$ and $F$ are constant, then $x\propto \frac{L}{A}$
For maximum displacement, area at which force applied should be minimum and vertical side should be maximum. This is given in the $R$ position of rectangular block.