Answer:
 2.068 x 10^6 m / s
Explanation:
radius, r = 5.92 x 10^-11 m 
mass of electron, m = 9.1 x 10^-31 kg 
charge of electron, q = 1.6 x 10^-19 C 
As the electron is revolving in a circular path, it experiences a centripetal force which is balanced by the electrostatic force between the electron and the nucleus. 
centripetal force = 
Electrostatic force = 
where, k be the Coulombic constant, k = 9 x 10^9 Nm^2 / C^2 
So, balancing both the forces we get 



v = 2.068 x 10^6 m / s 
Thus, the speed of the electron is give by  2.068 x 10^6 m / s.
 
        
             
        
        
        
If the applied force is in the same direction as the object's displacement, the work done on the object is:
W = Fd
W = work, F = force, d = displacement
Given values:
F = 45N
d = 12m
Plug in and solve for W:
W = 45(12)
W = 540J
 
        
             
        
        
        
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Answer:
Newton's law of universal gravitation states that every particle attracts every other particle in the universe with a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.
Explanation:
 
        
             
        
        
        
Answer:
P = 14700 J
Explanation:
Given that,
Mass of a piano, m = 75 kg
It is delivered throughout the window of a 6th story apartment which is 20 m above the ground.
We need to find the potential energy of the piano. It is given by :
P = mgh
Putting all the values,
P = 75 kg × 9.8 m/s² × 20 m
P = 14700 J
So, the potential energy of the piano is 14700 J.