A person travels by car from one city to another with differentconstant speeds b

Question

A person travels by car from one city to another with differentconstant speeds between pairs of cities. She drives for20.0 min at 75.0 km/h, 19.0 minat 75.0 km/h and 50.0 min at 35.0km/h, and spends 25.0 min eating lunchand buying gas. (a) Determine the average speed for thetrip.
1 km/h

(b) Determine the distance between the initial and final citiesalong this route.
2 km (a) Determine the average speed for thetrip.
1 km/h

(b) Determine the distance between the initial and final citiesalong this route.
2 km

Explanation / Answer

distance travel in 1 st 20 min is S = ( 75 km / h )* 20min                                                    = ( 75 km / h ) * ( 20 / 60 ) h                                                    = 25 km distance travel in next 19 min is S' = ( 75 km / h ) * ( 19/60) h                                                    = 23.75 km distance travel in last 50 min is S " = ( 35 km / h ) *( 50 / 60 ) h                                                     = 29.166 km lunch time t = 25 min total distance s = S + S' + S" = 77.91 km total time T = 20 min + 19 min +50 min + 25 min = 114min = ( 114 / 60 ) h = 1.9 h Average speed V = s / T                            = 41 km / h

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