Answer:
f = 0.75 Hz
Explanation:
It is given that, a person is kicking there legs three times every four seconds. We need to find his frequency. The number of times an event is occurring is called frequency of an object. The frequency of a person is given by :

So, the frequency of the person is 0.75 Hz. 
 
        
             
        
        
        
Instantaneous impulse and continuous force: these are the foundations of Newton laws. In short explanation; concept of force and mass.
 
        
                    
             
        
        
        
Explanation:
Power = work / time
Power = force × distance / time
P = (650 kg) (10 m/s²) (20 m) / (15 s)
P = 8667 W
 
        
             
        
        
        
Answer:
<h2>441 J</h2>
Explanation:
The potential energy of a body can be found by using the formula
PE = mgh
where
m is the mass
h is the height
g is the acceleration due to gravity which is 9.8 m/s²
From the question we have
PE = 30 × 9.8 × 1.5
We have the final answer as
<h3>441 J</h3>
Hope this helps you