A woman drives a car from one city to another with different constant speeds along the trip. She drives at a speed of 50.0 km/h for 15.0 min, 80.0 km/h for 25.0 min, makes a stop for 55.0 min, then continues at 40.0 km/h for 30.0 min, at which point she reaches her destination. Required:
a. What is the total distance between her starting point and destination (in km)?
b. What is the avg speed for the entire trip in (km/h)?

a) 65.83 km

b) 52.664 km/h

Explanation:

Different speed values :

Initial speed : 50 km/h  for 15 mins

                       80 km/h  for 25 mins

stops for 55 mins

40 km/h for 30 minutes

a) Determine total distance covered

Speed = distance covered / time

∴ Total distance = ∑speed * time

                           = ( 50 * 15/60 ) + ( 80*25/60) + ( 40 * 30/60 )

                           = 65.83 km

b) Average speed

Total distance / time taken

= 65.83 / ( 15 + 25 + 30 ) / 60

= 65.83 / ( 75/60)

= 52.664 km/h

prolly a beacuse the momentuem the car has increases while going down hill

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from wikipedia