Edescribe the meaning of a line crossing the x-axis in a
velocity-time graph.

A line crossing the x-axis in a velocity-time graph means that the moving object has changed its direction.

Explanation:

Velocity-Time graph:

A velocity-time graph is a two dimensional graph with velocity at its y-axis and time at its x-axis. At any point, value of y represents the velocity and value of x represents the time. The slope of the graph gives us the acceleration or deceleration of the moving object.

In a velocity-time graph:

- A straight line represents constant velocity.

- A diagonal line means that the velocity of a body is changing.

*Referring to the figure attached with the answer*

The velocity of the moving object increases at a constant rate for the first 10 minutes. Then the velocity is 60 m/min for the next 5 minutes. After that the velocity is decreasing. Till 30th minute when the velocity is at 0 m/min.

What happens here?

Velocity is a vector quantity. It has some direction. In a velocity-time graph, we are only concerned with two directions of velocity:

- Forward direction

- Backward direction

So, the object stops at 30th minute and starts moving in the reverse direction after that with an increasing velocity. The point where the line cuts the x-axis is basically the point where the object starts moving in the reverse direction.