Average speed, velocity and km/h ↔ m/s: Class 9 practice
Average speed = total distance ÷ total time; average velocity = displacement ÷ time. Read the method, follow the three worked examples, then try the six questions.
What you should know first
- Fractions
- Units of length and time
The idea behind average speed, velocity and km/h ↔ m/s
Average speed = total distance ÷ total time; average velocity = displacement ÷ time. To convert km/h to m/s divide by 3.6; m/s to km/h multiply by 3.6.
Step-by-step method
- Find total distance (or displacement) and total time.
- Divide.
- Convert units with ÷ 3.6 or × 3.6.
Worked example 1 (Basic)
Convert 216 km/h to m/s.
- 216 ÷ 3.6
- = 60 m/s
- Answer: 60 m/s
Worked example 2 (Standard)
A car goes 80 km at 20 km/h and returns at 15 km/h. Find its average speed for the round trip.
- Time = 80/20 + 80/15 = 9.33 h
- Average speed = 160 ÷ 9.33 = 17.14 km/h
- Answer: 17.14 km/h
Worked example 3 (Challenge)
For the same round trip (60 km each way at 60 and 15 km/h), what is the average velocity?
- Displacement = 0 (back to start)
- Average velocity = 0
- Answer: 0 km/h
Common mistakes and misconceptions
- Averaging the two speeds
- Mixing km/h with m/s
Practice questions
- (Basic) Convert 486 km/h to m/s.
- (Basic) Convert 468 km/h to m/s.
- (Standard) A car goes 20 km at 40 km/h and returns at 15 km/h. Find its average speed for the round trip.
- (Standard) A car goes 70 km at 40 km/h and returns at 10 km/h. Find its average speed for the round trip.
- (Challenge) For the same round trip (40 km each way at 40 and 15 km/h), what is the average velocity?
- (Challenge) For the same round trip (80 km each way at 30 and 30 km/h), what is the average velocity?
Answer key with full working
- Q1: 486 ÷ 3.6 → = 135 m/s → Answer: 135 m/s
- Q2: 468 ÷ 3.6 → = 130 m/s → Answer: 130 m/s
- Q3: Time = 20/40 + 20/15 = 1.83 h → Average speed = 40 ÷ 1.83 = 21.82 km/h → Answer: 21.82 km/h
- Q4: Time = 70/40 + 70/10 = 8.75 h → Average speed = 140 ÷ 8.75 = 16 km/h → Answer: 16 km/h
- Q5: Displacement = 0 (back to start) → Average velocity = 0 → Answer: 0 km/h
- Q6: Displacement = 0 (back to start) → Average velocity = 0 → Answer: 0 km/h
Syllabus note
This skill is listed under "Motion" for Class 9 in the NCERT/CBSE books. ICSE, IGCSE, IB and state boards may teach it in a different chapter or year.
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.
Related practice and notes
Frequently asked questions
Which chapter is average speed, velocity and km/h ↔ m/s in?
"Motion", Class 9 Physics (NCERT/CBSE). Other boards may place it differently.
How were the answers checked?
Answers on this page are generated and automatically re-checked by a second, independent calculation. They have not been reviewed by a teacher — if you spot a problem, tell us on WhatsApp.