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CBSE Class 9 Answered

A body travels from A to B in 10 seconds with a speed of 50 km/h and returns with a speed of 100 km/h in 5 s. Find the average speed. Also find the average velocity for the whole journey.
Asked by Topperlearning User | 10 Jun, 2016, 09:53: AM
answered-by-expert Expert Answer

Distance from A to B = Speed x time
                             = 50 km/h x 10 s

                             =(50 km/h x 10 s) x (5/18) .... (to convert km/h to m/s multiply by 5/18)

                             =1250 / 9

                             =139 m

Total distance from A to B both ways = 139 m × 2 = 278 m


Total time taken = 10 + 5 = 15 s


begin mathsize 12px style Average space speed space equals fraction numerator Total space distance space over denominator space Total space time end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals fraction numerator 278 space straight m over denominator 15 space straight s end fraction rightwards arrow Average space speed space equals 18.5 space straight m divided by straight s Average space velocity equals fraction numerator Displacement space over denominator space Time end fraction space space space space space space space space space space space space space space space space space space space space space space space space space space space space space equals 0 over time rightwards arrow Average space velocity equals 0 space km divided by straight h end style

Displacement is zero, because the body has come back to its initial position.

Answered by | 10 Jun, 2016, 11:53: AM

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