Question

Three rigid rods are joined to form an equilateral triangle ABC of side 1 m. Three particles carrying charges 20 μC each are attached to the vertices of the triangle. The whole system is at rest in an inertial frame. The magnitude of the resultant force on the charged particle at A is
(a) zero
(b) 3.6 N
(c) 3.6√3 N
(d) 7.2 N

Answer 1

The magnitude of the resultant force on the charged particle at A is

(a) Zero

This can be calculated as follows:

• We know that,

F= M * a

• As per question, the whole system is at rest in the inertial frame.

• This means, there is no movement.

• So, acceleration (a) =0

⇒ F = m (0)

       = 0

• Thus, force will also be zero.

Answer 2

The resultant force’s magnitude on the charged particle at A is zero.  

Explanation:

For the system, the net acceleration is zero. So, the resultant force should be zero.

We know that $\mathrm{F}_{-}\{\mathrm{net}\}=\mathrm{ma}$

$Fnet =m a$

where a is the charge’s acceleration of the particle at A. The value of a is zero, thus it can be concluded that the net force will be zero.

So, $F_{-}\{\text {net }\}=0$

$Fnet =0$