Question

During the first 14 minutes of a 1.0 hour trip, a car has an average speed 36 km/h. What must the average speed in km/h of the car during the rest of the trip be if the car is to have an average speed of 74.0 km/h for the entire trip

Answer 1

85.5 km/h

Step-by-step explanation:

`t_(1)` = time interval for first phase = 14 min =
`(14)/(60)` h = 0.233 h

`t_(2)` = time interval for second phase = 46 min =
`(46)/(60)` h = 0.767 h

`v` = average speed for the entire trip = 74 km/h

`v_(1)` = average speed in first phase = 36 km/h

`v_(2)` = average speed in second phase

`d_(1)` = distance traveled in first phase

`d_(2)` = distance traveled in first phase

average speed is given as

`v = (d_(1) + d_(2))/(t_(1) + t_(2))`

`v = (v_(1) t_(1) + v_(2) t_(2))/(t_(1) + t_(2))`

`74 = ((36) (0.233) + v_(2) (0.767))/(0.233 + 0.767)`

`74 = (36) (0.233) + v_(2) (0.767)`

`v_(2) = 85.5` km/h