Answer:
V=15.3 m/s
Explanation:
To solve this problem, we have to use the energy conservation theorem:

the elastic potencial energy is given by:

The work is defined as:

this work is negative because is opposite to the movement.
The gravitational potencial energy at 2.5 m aboves is given by:

the gravitational potential energy at the ground and the kinetic energy at the begining are 0.

I would assume that the magnesium would have to come into contact with an ion in order to become a magnesium ion.
The question is somewhat ambiguous.
-- It's hard to tell whether it's asking about '3 cubic meters'
or (3m)³ which is actually 27 cubic meters.
-- It's hard to tell whether it's asking about '100 cubic feet'
or (100 ft)³ which is actually 1 million cubic feet.
I'm going to make an assumption, and then proceed to
answer the question that I have invented.
I'm going to assume that the question is referring to
'three cubic meters' and 'one hundred cubic feet' .
OK. We'll obviously need to convert some units here.
I've decided to convert the meters into feet.
For 1 meter, I always use 3.28084 feet.
Then (1 meter)³ = 1 cubic meter = (3.28084 ft)³ = 35.31 cubic feet.
So 3 cubic meters = (3 x 35.31 cubic feet) = 105.9 cubic feet.
That's more volume than 100 cubic feet.