Answer:
The value is 
Explanation:
From the question we are told that
The mass of the car is
The period of the circular motion is 
The radius is 
Generally the frequency of the circular motion is

=> 
=> 
Answer:

Explanation:
We know that charge on electron

r= 2 nm
We know that force between two charge given

Now by putting the value


We know that mass of electron
The mass of electron

F= m a
a= Acceleration of electron
a= F/m


initial velocity given that zero ,u=0


Answer:
D. gravity
Explanation:
Gravity keeps the atmosphere from escaping into space.
I'd guess at valve B. more information about the interesting question would help.