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Question
A distance of 14.4 km is covered in 2 hours 40 minutes. Find the speed in ms−1. With this speed Sakshi goes to her school, 240 m away from her house, and then returns back. How much time, in all, will Sakshi take?
Solution
Distance = 14.4 km
Time taken to cover = 2 hrs 40 min
= `2 2/3=8/3` hrs
(i) ∴ speed in ms−1 = `(14.4xx1000)/(8/3xx3600)`
= `(144xx1000xx3)/(10xx8xx3600)=3/2`ms−1
= 1.5 ms−1
(ii) Distance from house to school and back
= 240 + 240 = 480 m
∴ Time taken = `480/1.5` second
= `(480xx10)/15` = 320 seconds
= `320/60` min = 50 min 20 sec
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