A bullet moving with a speed of 100 ~ms ⁻¹ can just penetrate two planks of equal thickness, then the number of such planks penetrated by the same bullet when the speed is doubled will be

Step-by-step solution

Given, u₁=100 ~ms ⁻¹ u₂=2 u₁=2 100=200 ~ms ⁻¹ Using equation of motion, v²=u²-2 a s ( acceleration is negative ) As, final velocity, v=0 u²=2 a s or s= u² 2 a s u² s₁ s₂ = u₁² u₂² = (100)² (200)² = 1 4 s₂=4 s₁=4 2 planks =8 planks