Question 59:
A car travels 100 km at a speed of 60 km/h and returns with a speed of 40 km/h. Calculate the average speed for the whole journey.
Lakhmir Singh Physics Class 9
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Time taken to go = 100/60 = 5/3hr
Time taken to return = 100/40 = 5/2 hr
Total distance = ( 100 + 100 ) km = 200 km
Total time taken = ( 5/3 + 5/2 ) hr = 25/6 hr
Average speed = total distance / total time
= 200 / 25 / 6
= 200 × 6/25
= 48 km/hr
Hence average speed is 48 km/hr
Time taken to return = 100/40 = 5/2 hr
Total distance = ( 100 + 100 ) km = 200 km
Total time taken = ( 5/3 + 5/2 ) hr = 25/6 hr
Average speed = total distance / total time
= 200 / 25 / 6
= 200 × 6/25
= 48 km/hr
Hence average speed is 48 km/hr
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