# NCERT Question 3 - Chapter 8 Class 9 - Motion (Term 1)

Last updated at June 6, 2019 by Teachoo

Class 9

Chapter 8 Class 9 - Motion (Term 1)

NCERT Question 3 Abdul, while driving to school, computes the average speed for his trip to be 20 km hβ1. On his return trip along the same route, there is less traffic and the average speed is 30 km hβ1. What is the average speed for Abdulβs trip? We know that Average speed = (πππ‘ππ πππ π‘ππππ)/(πππ‘ππ π‘πππ) Let Distance between Abdulβs 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·ππ π‘ππππ/ππππ 20 = π/ππππ β΄ Time = π/20 School to Home Distance = d Speed = 30 km/h Speed = π·ππ π‘ππππ/ππππ 30 = π/ππππ β΄ Time = π/30 Total time taken = π/20 + π/30 = (3π + 2π)/60 = 5π/60 = π/12 Average speed = (πππ‘ππ πππ ππ‘πππ)/(πππ‘ππ π‘πππ) = 2π/(π/12) = (2π Γ 12)/π = 24 km/h