Question

a bullet moving with a velocityof 100m/s can just penetrate two planks of equal thickness. thenumber of such planks penetrated by the same bullet when the velocity is doubled will be

Answer 1

3rd equation of motion can be be applied: v^2 = u^2 + 2as, where acceleration is -ve. Hence v^2 = u^2 – 2as.
v, final velocity = 0. Therefore, u^2 = 2as.
i.e. s is proportional to u^2. → s1÷ s2 = u1^2 ÷ u2^2
Therefore, s2 = (u2^2 ÷ u1^2) x s1 = (200÷100)^2 x 2 (planks) = 8 planks
Answer is 8

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Answer 2

S be no. Of one plate

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Diagram is only for reference not necessary