A bullet is fired into a fixed target looses one third of its velocity after travelling 4 cm. It penetrates further D × 10⁻³ m before coming to rest. The value of D is :
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A bullet is fired into a fixed target looses one third of its velocity after travelling 4 cm. It penetrates further D × 10⁻³ m before coming to rest. The value of D is :

G1 Physics · Accepted Answer

v² - u² = 2aS After travelling 4 cm, speed becomes 2u/3. (2u/3)² - u² = 2a(4 × 10⁻²) 4u²/9 - u² = 8a × 10⁻² -5u²/9 = 8a × 10⁻² ...(1) For the remaining penetration x: 0 - (2u/3)² = 2ax -4u²/9 = 2ax ...(2) Dividing (1) by (2): (5/4) = (4 × 10⁻²)/x x = (16/5) × 10⁻² m = 3.2 × 10⁻² m = 32 × 10⁻³ m Thus D = 32. The source paper marks this question as BONUS because no listed option matches D = 32. For upload compatibility, Option A is filled as a placeholder.