Equations Of Motion

Drawing from NCERT Class 11, Chapter 3 (Motion in a Straight Line), when an object decelerates uniformly to rest, the third equation of motion v² = u² − 2as applies, where the final velocity v is zero. Rearranging gives the stopping distance s = u² / (2a). Substituting u = 30 m/s and a = 5 m/s² yields s = (30)² / (2 × 5) = 900/10 = 90 m. The option 60 m comes from incorrectly using u²/(2a) with u taken as a smaller value or dividing by 15. The option 120 m overestimates by using 2u instead of u² scaling. The option 45 m halves the correct answer, likely from forgetting to square the initial velocity properly. Plausibility check: the time to stop is u/a = 6 s, and the average velocity during braking is 15 m/s, so distance equals 15 × 6 = 90 m, which agrees exactly with the kinematic equation result.