Hi there!
Assuming the track is frictionless:

Cancel out the masses and rearrange to solve for velocity:

Plug in the given height and let g = 9.8 m/s²:

Any object that is spherical in shape would best represent a true scale model of the shape of the Earth. Examples are ping pong balls, billiard balls, marble and other smooth spherical objects. The shape of the Earth is called the oblate spheroid. The "oblate" would refer to an oblong shape and "spheroid" would refer to an almost spherical shape. The earth has on almost spherical shape and has a slightly oblong appearance. The diameter from the South pole to the north pole was measured to have a value of 12714 km while the diameter of the equator is approximately 12756 km. As you can see, the values are not equal. This makes the earth not a perfect sphere.
For both NPN and PNP this is true:
The base is between the collector and the emitter.
They size of the wave and the time of a certain wave.