# A man travels first 50 km at 25 km/h, next 40 km at 20 km/h and then 90 km at 15 km/h. His average speed for the whole journey (m/s) is -

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A man travels first 50 km at 25 km/h, next 40 km at 20 km/h and then 90 km at 15 km/h. His average speed for the whole journey (m/s) is -

1. 18 m/s
2. 5 m/s
3. 10 m/s
4. 36 m/s

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Correct Answer - Option 2 : 5 m/s

Given

A man travels first 50 km at 25 km/h, next 40 km at 20 km/h and then 90 km at 15 km/h.

Concept used

Average speed = (Total Distance) / Time taken

Calculation

T1 = 50/25 = 2 hr

T2 = 40/20 = 2 hr

T3 = 90/15 = 6 hr

Average speed

⇒ $\frac{{50\ +\ 40\ +\ 90}}{{2\ +\ 2\ +\ 6}}$

⇒ 18 km/hr

To convert it into m/s multiply with (5/18)

⇒ 18 × (5/18)

∴ 5 m/s