(3). The magnitude of the electrostatic force
between two point charges is F. If the distance
between the charges is double, what will
electrostatic force between the charges become?
Explain

Explanation:

mass of proton = m

initial velocity, u1 = 1.80 x 10^7 m/s

final velocity, v1 = - 1.5 x 10^7 m/s

(a)

Let m' is the mass of unknown nucleus.

By use of conservation of energy

m' = 11 m

Thus, the mass of unknown nucleus is 11 times the mass of proton.

(b)

By use of conservation of momentum

m x u1 + m' x 0 = m x v1 + m' x v'

where, v' is the velocity of unknown nucleus after collision

m x 1.8 x 10^7 = - m x 1.5 x 10^7 + 11 m x v'

3.3 m x 10^7 = 11 m x v'

v' = 3 x 10^6 m/s  

Thus, the velocity of unknown nucleus after collision is 3 x 10^6 m/s