20 is the atomic number for Calcium.
<span>Magma is composed of molten rock and is stored in the Earth's crust. Lava is magma that reaches the surface of our planet through a volcano vent. Lavaflow, Hawai</span>
Answer:
<em>Choice: c. 6sec</em>
Explanation:
<u>Horizontal Launch
</u>
When an object is thrown horizontally with a speed (v) from a height (h), it describes a curved path ruled by gravity until it finally hits the ground.
The horizontal component of the velocity is always constant because no acceleration exists in that direction, thus:

The vertical component of the velocity changes in time because gravity makes the object fall at increasing speed given by:

Where 
To calculate the time the object takes to hit the ground, we use the same formula as for free-fall, since the time does not depend on the initial speed:

The marble rolls the edge of the table at a height of h=180 m, thus:


t = 6 sec
Choice: c. 6sec
C it reduces the amount of useful work done on objects move it up the ramp