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Two cars, A and B, start from the same place. A take the direction of the north with a constant velocity of 80 km/h, and B the direction of the east, with an acceleration of 4 m/s2 (start from the rest). After 13 seconds, which is the relative velocity of the car A in reference to B?

**Solution with FisicaLab**

Erase the content of the chalkboard. And add one element Mobile in X, one element Mobile in Y with constant velocity, one element Relative velocity, and one element Stationary reference system. As show the image below:

We assume that the car A take the direction of the positive Y axis, and car B the direction of the positive X axis. And that both cars start from the origin. Now, as we know the end time, in the element Stationary reference system, write:

**tf**13

To the element Mobile in Y with constant velocity, we call this car *Car A*, write:

**Name**Car A

**yi**0

**yf**yf

**ti**0

**vy**80 @ km/h

To the element Mobile in X, we call this car *Car B*:

**Name**Car B

**ax**4

**xi**0

**vxi**0

**ti**0

**xf**xf

**vxf**vxf

And to the element Relative velocity:

**Object 1**Car A

**Object 2**Car B

**v**v

**ang**ang

Where the magnitude and the angle of the relative velocity are unknown data. Now click in the icon Solve to get the answer:

v = 56.549 m/s ; ang = 156.861 degrees ; xf = 338.000 m ; vxf = 52.000 m/s ; yf = 288.889 m ; Status = success.

The desired data are v = 56.549 m/s and ang = 156.861 degrees.

Next: Example 7 (k), Previous: Example 5 (k), Up: Examples kinematics of particles [Contents][Index]