# Help with vectors and 2-dimentisonal motion: relative velocity

1. Nov 13, 2005

### xkamranx

A science student is riding on a flatcar of a train traveling along a straight horizontal track at a constant speed of 10 m/s. The student throws a ball along a path that he judges to make an initial angle of 60° with the horizontal and to be in line with the track. The student’s professor, who is standing on the ground nearby, observes the ball to rise vertically. How high does the ball rise?

Thanks a lot.

Last edited: Nov 13, 2005
2. Nov 13, 2005

### xkamranx

anyone haev any idea?

3. Nov 13, 2005

### SN1987a

The basic principle for this problem would be to use the Galilean transformation for inertial frames. In simpler words, if you know the velocity of an object in a moving frame, what is the velocity of that same object in a stationary frame?

Once you know this, you can use it's inverse into your problem. Knowing the apparent velocity in the stationary frame, what is the velocity in the moving frame?

4. Nov 13, 2005

### dx

The train is moving with a speed of 10 m/s . The balls horizontal velocity is
$$v\sin{60}$$. From the ground, the horizontal velocity is zero. Can you calculate the magnitude of the balls velocty from this?