A car travels the first 50km of its journey at an average speed of 25m/s and the next 120 at an average speed of 80km/h. The car completes the last part of its journey at an average speed of 90km/h in 35minutes. Find the average speed for its entire journey,giving your answer in km/h.
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Step-by-step explanation:
A car travels the first 50km of its journey at an average speed of 25m/s
25 m/s = 25 * 3600 /1000 = 90 km /hr
Time = Distance / Speed
Time = 50/90 = 5/9 hr
next 120 km at an average speed of 80km/h
=> Time = 120/80 = 3/2 hr
last part of its journey at an average speed of 90km/h in 35 Minutes
time = 35 minutes = 35/60 hr = 7/12 hr
Distance covered = 90 * 7 /12 = 105/2 km
Total Distance = 50 + 120 + 105/2 = 435/2 km
Total time = 5/9 + 3/2 + 7/12 = ( 20 + 54 + 21) /36 = 95/36
Average speed = (435/2)/(95 /36) = 432 * 18 /95 = 81.85 km/hr
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