Explanation:
Given that,
Weight of the friend, W = 600 N 
When the friend sits on the metal frame it bends downward 4 cm, we can say that the compression in the it is 4 cm or 0.04 m
To find,
Spring constant for this chair or k
Solve :
The weight of an object is equal to the force exerted by the gravitational force, F = 600 N
According to Hooke's law, the force exerted by the spring is given by :
F = kx
k is the spring constant


k = 15000 N/m
Therefore, the spring constant of the spring is 15000 N/m.
 
        
             
        
        
        
The answer is 
C. They have all ready achieved high levels of cardio respiratory fitness.
        
             
        
        
        
Mechanical advantage is defined as the ratio of output load to the input load. The mechanical advantage of the machine will be 0.1.
<h3>What is 
mechanical advantage?</h3>
Mechanical advantage is a measure of the ratio of output force to input force in a system, 
It is used to obtain the efficiency of forces in levers and pulleys. It is an effective way of amplifying the force in simple machines like levers.
The theoretical mechanical advantage is defined as the ratio of the force responsible for the useful work in the system to the applied force. 
Given
applied force = 250 N
Output force = 25 
Mechanical advantage = work output / work input
 


Hence the mechanical advantage of the machine will be 0.1
To learn more about the mechanical advantage refer to the link;
brainly.com/question/7638820
 
 
 
        
             
        
        
        
Milliliters if you're doing science. 
        
             
        
        
        
Dark energy is a theoretical repulsive energy that causes the acceleration to the expansion of the universe. Among the choices, the nearest answer would be D. Dark energy can also be defined as a new form of energy, that is a dynamic field that fills up space but has an effect opposite to that of normal energy.