The voltage between the cathode and the screen of a television set is 30 kV. If we assume a speed of zero for an electron as it leaves the cathode, what is its speed (m/s) just before it hits the screen

The speed is  

Explanation:

From the question we are told that

      The  voltage  is  

      The  initial velocity of the electron is  

Generally according to the law of energy conservation

    Electric potential Energy  =  Kinetic energy of the electron

So  

Where  

Here  m is the mass of the electron with a value of  

     and  

      Here  e is the charge on the electron with a value  

=>    

=>      

substituting values  

answer: b.

explanation: