Complete Question 
The complete question is shown on the first uploaded image 
Answer:
a 
The torque produced by the pile of rocks is  
   
b
 The distance of the single for equilibrium to occur is  
 
Explanation:
From the question we are told that 
      The mass of the left rock is  
      The mass of the rock on the right 
     The distance from  fulcrum to the center of the pile of rocks is  
    
Generally the torque produced by the pile of rock is mathematically represented as
            
Substituting values 
           
                  
            
      
 Generally we can mathematically evaluated the distance of the the single rock that would put the system in equilibrium as follows 
    The torque due to the single rock is 
            
At equilibrium the both torque are equal 
             
Making  the subject of the formula
 the subject of the formula 
              
Substituting values 
              
 
              
 
 
        
             
        
        
        
Answer:
15.76N
Explanation:
horizontal component =Fcos¢ = 20cos38 = 15.76N
 
        
                    
             
        
        
        
Answer:
A. chemical substance whose atoms all have the same number of protons
Explanation:
An element is a substance which contains identical atoms that have the same number of protons in the nucleus.
Elements are arranged in the periodic table according to their atomic number (= number of protons): so atoms of different elements have a different number of protons in their nuclei.
For a neutral atom, the number of electrons around the nucleus is also equal to the number of protons.
Moreover, atoms of the same element can have a different number of neutrons, despite having the same number of protons - these atoms are called isotopes.
 
        
             
        
        
        
I’m pretty sure it just wants you to list the property’s meaning the material and density
        
             
        
        
        
GPE=mgh
 =25 x 10 x 3
 =750J