Answer:
The time take is  
Explanation:
From the question we are told that 
     The decay constant is   
 
      The percentage fall is  
The equation for radioactive decay is mathematically represented as 
                
Where is  is the new amount of the new the isotope while
 is the new amount of the new the isotope while  is the original
 is the original 
At initial   %  = 1
%  = 1 
At  %  = 0.80
%  = 0.80  
        
=>     
=>     
 
        
                    
             
        
        
        
the radius of the entire atom was 0.00000001 cm.
 
        
                    
             
        
        
        
Answer: 
Explanation:
The acceleration of the motorcycle is given by

where
v=24 m/s is the final velocity of the motorcycle
u=15 m/s is the initial velocity
t=3 s is the time taken
Substituting these numbers into the equation, we find

 
        
                    
             
        
        
        
Hope this shows! It has all the equations for all of the problems u asked in the comments