The particle in the air match the mass with the particles around the balloon stoping it from floating any higher
E=F*d/2 = M*g*d/2 = 25kg * 9.8 N/kg *0.65m / 2 = 79.625J
Answers is F=7.84 N
Friction force resists the effect of horizontal force and trying to approch to a limiting force.
we have formula for limiting friction force between block and floor
F=Ц N
where N=mg
putting values we get answer.
Incomplete question as we have not told to find what quantity.The complete question is here
A spherical capacitor contains a charge of 3.50 nC when connected to a potential difference of 210.0 V. Its plates are separated by vacuum and the inner radius of the outer shell is 5.00 cm.calculate: (a) the capacitance; (b) the radius of the inner sphere; (c) the electric field just outside the surface of the inner sphere.
Answer:
(a) 
(b) 
(c)
Explanation:
Given data

For part (a)
The Capacitance given by:

For part (b)
The Capacitance of coordinates is given as

For part (c)
The electric field according to Gauss Law is given by:

Answer:
a) 
b) 
Explanation:
Part a
For this case we can begin finding the period like this:

Then we know that the centripetal acceleration is given by:

And the velocity is given by:

If we replace this into the acceleration we got:

And we can replace the values and we got:

Part b
For this case we want to find a value of k such that:

Where a = 9.74, so then we can solve for k like this:
