Answer to Question #15630 in Mechanics | Relativity for martina

Question

sally travels by car from one city to other.she drives for 30.0 min at 80,0 km/h,120 min at 150 km/h ,and 45.0 min at 40.0 km/h and she speeds 15.0 min eating lunch and buying gas.
a:determine the avrage speed for the trip.
b:determine the total distance traveled.

Answer 1

b). The total distance traveled is

D = 80[km/h]*30[m] + 150[km/h]*120[m] + 40[km/h]*45[m] =
& = 80[km/h]*0.5[h] + 150[km/h]*2[h] + 40[km/h]*0.75[h] =
& = 370 km.

a). The total time elapsed is

T = 30[m] + 120[m] + 45[m] + 15[m] =
& = 0.5[h] + 2[h] + 0.75[h] + 0.25[h] =
& = 3.5 h.

So, the average speed was

V = D/T = 370[km]/3.5[h] ≈ 105.7 km/h.