Balance would be the answer to this questions
Answer:

8.57181 s
84.0894561 m/s
Explanation:
t = Time taken
u = Initial velocity
v = Final velocity
s = Displacement
g = Acceleration due to gravity = 9.81 m/s² = a
Let distance from ground be x
From equation of motion we have

Here, distance covered while the stone is falling will be 

The equation is 
At the ground x = 0

The time taken by the stone to fall to the ground is 8.57181 s

The velocity of the stone when it reaches the ground is 84.0894561 m/s
Work=force X distance
Newtons is a measurement of force
4 meters is your distance 60×4=240
240 joules
It is 800 N FN = 600N + 200 N = 800 N Answer to your question: The net force is all Newton's second law. It is the force that acts on a body or a particle. for example: It is the force we make when we push a car or something heavy that is in a straight line. .
As waves get closer to the beach they increase in energy