3.2 Example 2

A car start from a place B with a constant velocity of 75 km/h at the east. 8 minutes after, other car with a constant velocity of 88 km/h start from a place A to the east. The place A is 5 km to the west of B. How minutes needs the last car to reach the first car? In that moment, which is the distance between the place A and the cars?

Solution with FisicaLab

Select the Kinematic group and, inside this, the Particles module. Erase the content of the chalkboard. And add two elements Mobile in X with constant velocity and one element Stationary reference system. As show the image below:

We assume that the Mobile in X at the left, corresponds to the car that start from A. Now, the end time, is an unknown data, then in the element Stationary reference system write:

tf

t @ min

Because we want the end time in minutes. Now, we assume that the car that start from A is in the origin of the stationary reference system, and start at 8 minutes. We call this car Car A:

Name

Car A

xi

0

xf

d @ km

ti

8 @ min

vx

88 @ km/h

To the car that start from B. Its initial X coordinate is 5 km (because the other car is in the origin), and the start time is 0. We call this car Car B:

Name

Car B

xi

5 @ km

xf

d @ km

ti

0

vx

75 @ km/h

The final X coordinate of both cars is the same, because we want know the moment when the last car reach the first car. Now click in the icon Solve to get the answer.

d = 101.538 k m ;  t = 77.231 min ;
Status = success.