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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 4 6 8 10
8velocity is doubled means kinetic energy is made 4 times
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 ÷ u2^2Therefore, s2 = (u2^2 ÷ u1^2) x s1 = (200÷100)^2 x 2 (planks) = 8 planksAnswer is 8
Let the velocity be V and thickness be h ( initial) H (final) NowV^2=2gh. h= thicknessAgaina (2v)^2=2gH4v^2=2gH4*2gh=2gH4h=HH=8 . h=2plancks
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