As per the question, the point charge is given as [q] = 6.8 C
The velocity of the charged particle [v] = 
The magnetic field [B] = 1.4 T
The angle made between magnetic field and velocity
= 15 degree.
We are asked to calculate the magnetic force experienced by the charged particle.
The magnetic force experienced by the charged particle is calculated as -
Magnetic force 
i.e F = 





Hence, the force experienced by the charged particle is C i.e 
Remember opposites attract and same charges repel each other.
Object A= negatively charged.
Object A and B attract so B must be positively charged.
Object B and C repel so because B is positively charged C must also be positively charged.
Object C and D attract and because C is positively charged, D must be negatively charged.
Answer:
The frequency of oscillation of the simple pendulum is 0.49 Hz.
Explanation:
Given that,
Mass of the simple pendulum, m = 0.35 kg
Length of the string to which it is attached, l = 1 m
We need to find the frequency of oscillation. The frequency of oscillation of the simple pendulum is given by :

So, the frequency of oscillation of the simple pendulum is 0.49 Hz. Hence, this is the required solution.