a boy for 10 minutes at a uniform speed of 9km h. At what speed should he run for the next 20 minutes so that the average speed 12 km h
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13 is the right answer
Deepakbehl:
13.5 answer
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Distance travelled in 10 minutes
S1 = 9 km/h × 10 minutes × 1/(60 minutes / h) ……[∵ Distance = speed × Time]
S1 = 1.5 km
Distance travelled in next 20 min
S2 = v × 20 minutes / (60 minutes / h)
S2 = v/3
Average speed = Total distance / Time
12 = (1.5 + v/3) / [(10 + 20)/60]
12 = (1.5 + v/3) / (1/2)
6 = 1.5 + v/3
v/3 = 4.5
v = 13.5 m/s
He should run with speed of 13.5 m/s
S1 = 9 km/h × 10 minutes × 1/(60 minutes / h) ……[∵ Distance = speed × Time]
S1 = 1.5 km
Distance travelled in next 20 min
S2 = v × 20 minutes / (60 minutes / h)
S2 = v/3
Average speed = Total distance / Time
12 = (1.5 + v/3) / [(10 + 20)/60]
12 = (1.5 + v/3) / (1/2)
6 = 1.5 + v/3
v/3 = 4.5
v = 13.5 m/s
He should run with speed of 13.5 m/s
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