Answer:
54mph
Step-by-step explanation:
[tex] \textsf {\underline {To find :-}}[/tex]
The average speed at 2nd departure.
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[tex] \textsf{ \underline {Given :-}}[/tex]
The speed during 90 miles travel = 70mph
The average speed during the entire journey = 63mph
The distance in second departure = 70 miles
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[tex] \textsf {\large{ \underline{ Solution :-}}}[/tex]
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The distance travelled in the entire journey
= 90 + 70 = 160 miles.
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Then the time taken in entire journey will be
[tex] \sf \large = \frac{total \: distance}{average \: speed} \\ \\ \sf \large = \frac{160}{63} \\ \\ \sf \large = 2 \frac{37}{63}hours \\ \\ \sf \large = 2 \: hours \: 35 \: minutes[/tex]
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Time taken at first departure
[tex] \sf \large = \frac{distance}{speed} \\ \\ \sf \large = \frac{9 \cancel0 }{7 \cancel0} \\ \\ \sf \large = 1 \frac{2}{7} \: hours \\ \\ \sf \large = 1 \: hour \: 17 \: minutes[/tex]
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Time taken in second departure
= 2 hours 35 minutes - 1 hour 17 minutes
= 1 hour 18 minutes
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Speed at second departure will be
[tex] = \sf \large \frac{distance}{time} \\ \\ \sf \large = \frac{70}{1 \frac{18}{60} } \\ \\ \sf \large = \frac{70}{1.3} \\ \\ \sf \large = 53.84 \: mph \\ \\ \sf \large = 54 \: mph[/tex]
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The average speed at second departure was 54mph.
