A car has side window made of glass (shear strength 40 M Pa) having size $40 c m \times 40 c m .$ The car is travelling with a velocity of $40 m / s$ in still air. Density of air can be assumed to be $1.25 k g / m^{3} .$ The windows are closed.

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If the glass is very thin, it may break & fall out of the car.

If we want that glass should not break, it's thickness should be greater than $2.5 μ m .$

If we want that glass should not break, it's thickness should be greater than $8.75 μ m .$

If the glass is very thin, it may break and fall into the car.

answer is B, C.

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Detailed Solution

Applying Bernaullis theorem from the frame of car.

$P_{i n} + 0 = P_{o u t} + \frac{1}{2} ρ v^{2}$

Again $(P_{i n} - P_{o u t}) \times {(0.4)}^{2} = σ \times 1.6 \times t$

$\Rightarrow \frac{1}{2} ρ v^{2} \times 0.16 = 4 \times 10^{7} \times 1.6 t \Rightarrow \frac{1}{2} \times \frac{1.25 \times 40 \times 40 \times 0.16}{1.60 \times 4 \times 10^{7}} = t$

$t = 2.5 μ m$

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