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Last updated at May 23, 2019 by Teachoo

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Page 103 Q2 A bus decreases its speed from 80 km h–1 to 60 km h–1 in 5 s. Find the acceleration of the bus. Initial velocity of the bus = u = 80 km/h Final velocity of the bus = v = 60 km/h Time taken = t = 5s Since time is in seconds, we convert the initial & final velocity in m/s. Conversion from km/h to m/s 1 km = 1000 m 1 hour = 60 minutes = 3600 s ∴ (1 𝑘𝑚)/ℎ = (1000 𝑚)/(3600 𝑠) ∴ 1 km/h = 5/18 m/s Initial velocity = u = 80 km/h = 80 × 5/18 = 400/18 m/s Final velocity = v = 60 km/h = 60 × 5/18 = 300/18 m/s Acceleration = (𝐹𝑖𝑛𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 − 𝐼𝑛𝑖𝑡𝑖𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦)/𝑇𝑖𝑚𝑒 = (𝑣 − 𝑢)/𝑡 = (300/18 − 400/18)/5 = ((−100)/18)/5 = (−100)/(18 × 5) Note: Negative sign of acceleration means that velocity is decreasing

Questions from Inside the chapter

Question 1 Page 100

Question 2 Page 100

Question 3 Page 100

Difference between speed and velocity (Question 1 Page 102)

Question 2 Page 102

Question 3 Page 102

Question 4 Page 102

Question 5 Page 102

Question 1 Page 103

Question 2 Page 103 You are here

Question 3 Page 103

Question 1 Page 107

Question 2 Page 107

Question 3 Page 107

Question 4 Page 107

Question 1 Page 109

Question 2 Page 110

Question 3 Page 110

Question 4 Page 110

Question 5 Page 110

Class 9

Chapter 8 Class 9 - Motion

About the Author

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 9 years. He provides courses for Maths and Science at Teachoo.