Is the 9 planets in the world or has no one found another one

There are plenty more than 9 planets in the world. There are only 8 verified planets in our solar system.

Explanation:

The speed of the object at the lowest point in its trajectory is:

Explanation:

We can use the conservation of energy between the maximum point of swing and the lowest point of the pendulum.

(1)

Where:

We can find h using trigonometry.

Now, using equation (1) we can find v.

I hope it helps you!