A bullet of mass 0.04 kg moving at 90 m s⁻¹ is brought to rest by a wooden block over 60 cm. The average retarding force exerted by the block on the bullet is closest to:
A135 N
B180 N
C270 N
D540 N
Answer & Solution
Correct answer: C. 270 N
1. Use v² = u² − 2 a s with v = 0, u = 90 m s⁻¹, s = 0.6 m.
2. a = u² / (2 s) = (90)² / (1.2) = 6750 m s⁻² (retardation).
3. F = m a = 0.04 × 6750 = 270 N.
4. The distractors come from forgetting the factor of 2 (135 N) or doubling (540 N).
_Source: NCERT Class 11 Physics Ch 4 "Laws of Motion", Example 4.2, p. 55_
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