Part a
He firstly travels for 30 mins at 25 m/s
i.e. he travels for 30×60=1800seconds
The distance he travels will be 1800×25=45000m(45km)
His second set of travelling is for 20 minutes at 36 m/s
i.e. he travels for 20×60=1200seconds
The distance he travels will be 1200×36=43200m(43.2km)
The total distance he travels will be 45000+43200=88200m.
Part b
This means his average speed as the overall journey took one hour is
S=TD=360088200=24.5m/s
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