Practice question

Given: A 0.9 g drop falls from 150 m and hits the ground at 13 m/s . What is the work done by air resistance? (Take g = 10 m/s² ) These values define the system as per NCERT data. Formula: Work by gravity W_g = mgh = 0.0009 × 10 × 150 = 1.35 J. This is standard NCERT relation. Substitution & Calculation: Final K = 1/2 × 0.0009 × 13² = 0.07605 J . K_f = W_g + W_r Rightarrow 0.07605 = 1.35 + W_r Rightarrow W_r = -1.27395 J approx -1.27 J . Result: The computed value matches expected outcome and confirms correct choice as per NCERT.