Given that,
Mass of the stone, m = 400 g = 0.4 kg
Initial speed, u = 20 m/s
It is climbed to a height of 12 m.
To find,
The work done by the resistance force.
Solution,
Let v is the final speed. It can be calculated by using the conservation of energy.

Work done is equal to the change in kinetic energy. It can be given as follows :

So, the required work done is 32.99 J.
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Gravitational potential energy can be described as m*g*h (mass times gravity times height).
Originally,
15kg * 9.8m/s^2 *0.3 m = 44.1 kg*m^2/s^2 = 44.1 Joules.
After it is moved to a 1m shelf:
15kg * 9.8m/s * 1 = 147 kg*m^2/s^2= 147 Joules.
To find how much energy was added, we subtract final energy from initial energy:
147 J - 44.1 J = 102.9 Joules.
Energy can change form, but the total amount of energy stays the same.
In a oxidation-reduction reaction, the oxidizing agent always undergoes reduction.
TRUE.