A car drives north for 35 minutes at 85 km/hr and then stop for 15 mins. The car continues north traveling 130 km in 2 hours. What is the total displacement and average velocity?

1 Answer
Jul 4, 2015

Total displacement: 179.6 km
Average velocity: 63.4 km/h


Since it's travelling in the same direction for the entire duration of its journey, the total displacement of the car is simply the distance from the starting point.

In the first part of its journey, the car travelled for 35 minutes at a speed of 85 km/h. Convert the time from minutes to hours to get

#35cancel("min") * "1 h"/(60cancel("min")) = "0.5833 h"#

This means that the car covered

#0.5833cancel("h") * "85 km"/(1cancel("h")) = "49.6 km"#

The car stops, then continues along its current direction, covering 130 km in 2 hours. The total displacement of the car will thus be

#d_"total" = 49.6 + 130 = color(green)("179.6 km")#

The average velocity is simply the total dispalcement divided by the total time of travel. In your case, the total time will be

#t_"total" = "0.5833 h" + underbrace("0.25 h")_(color(blue)("= 15 min")) + "2 h" = "2.833 h"#

The average velocity is

#bar(v) = "179.6 km"/"2.833 h" = color(green)("63.4 km/h")#