The acceleration due to gravity serves as the centripetal acceleration of the objects that orbits the Earth. The centripetal acceleration due to gravity is calculated through the equation,
    a = v²/r
where v is the speed and r is the radius. Substituting the known values to the equation,
   9.8 m/s² = (420 m/s)² / r
The value of r from the equation is 18000 m or equal to 18 km.
<em>Answer: 18 km</em>
        
             
        
        
        
Answer
Explanation:
As the three resistors are connected in series, the expression to be used for the  
calculation of RT equivalent resistance
 is:  
RT = R1 + R2 + R3
We replace the data of the statement in the previous expression and it remains:  
5 10 15 RT + R1 + R2 + R3 + +
We perform the mathematical operations that lead us to the result we are looking for:  
RT - 30Ω
 
        
             
        
        
        
Answer: Bohr's model (1913)
   Niels Bohr improved Rutherford's model. Using mathematical ideas, he showed that electrons occupy shells or energy levels around the nucleus. The Dalton model has changed over time because of the discovery of subatomic particles.
Bohr's model (1913) 
   Niels Bohr improved Rutherford's model. Using mathematical ideas, he showed that electrons occupy shells or energy levels around the nucleus. The Dalton model has changed over time because of the discovery of subatomic particles
   Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass.
   John Dalton
The idea that everything is made of atoms was pioneered by John Dalton (1766-1844) in a book he published in 1808. He is sometimes called the "father" of atomic theory, but judging from this photo on the right "grandfather" might be a better term.
 
Explanation:
 
        
             
        
        
        
the average kinetic  energy of the particles in an object is directly proportional to its TEMPERATURE.