NCERT Questions

Class 9
Chapter 8 Class 9 - Motion

Get live Maths 1-on-1 Classs - Class 6 to 12

### Transcript

NCERT Question 3 Abdul, while driving to school, computes the average speed for his trip to be 20 km hβ1. On his return trip along the same route, there is less traffic and the average speed is 30 km hβ1. What is the average speed for Abdulβs trip? We know that Average speed = (πππ‘ππ πππ π‘ππππ)/(πππ‘ππ π‘πππ) Let Distance between Abdulβs Home and School be d Now, Since he goes from home to school, and then back Total Distance = d + d = 2d To find Total Time, we find Time taken to go from Home to School, and from School to Home Let time taken to reach home = π‘_2 Home to School Distance = d Speed = 20 km/h Speed = π·ππ π‘ππππ/ππππ 20 = π/ππππ β΄ Time = π/20 School to Home Distance = d Speed = 30 km/h Speed = π·ππ π‘ππππ/ππππ 30 = π/ππππ β΄ Time = π/30 Total time taken = π/20 + π/30 = (3π + 2π)/60 = 5π/60 = π/12 Average speed = (πππ‘ππ πππ ππ‘πππ)/(πππ‘ππ π‘πππ) = 2π/(π/12) = (2π Γ 12)/π = 24 km/h