Take the stone's position at ground level to be the origin, and the downward direction to be negative. Then its position in the air
at time
is given by

Let
be the depth of the well. The stone hits the bottom of the well after 5.00 s, so that

Answer: The formula used to solve the problems related to first law of thermodynamics is 
Explanation:
First law of thermodynamics states that the total energy of the system remains conserved. Energy can neither be destroyed, nor be created but it can only be transformed into one form to another.
Its implication is any change in the internal energy will be either due to heat energy or work energy.
Mathematically,

where, Q = heat energy
W = work energy
= Change in internal energy
Sign convention for these energies:
For Q: Heat absorbed will be positive and heat released will be negative.
For W: Work done by the system is negative and work done on the system is positive.
For
: When negative, internal energy is decreasing and when positive, internal energy is increasing.
Hence, the formula used to solve the problems related to first law of thermodynamics is 
The formula for average speed is

So we can just substitute our data.

- its the result
GPE I am assuming is gravitational potential energy. I'll denote it as U for simplicity.
U = mgy
U = (70kg)(9.81m/s^2)(1m) = 686.7J
U = 686.7J
Hope this helps!
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