Question

A bob of mass m is suspended from the ceiling of a train moving with an acceleration a as shown in figure. Find the angle $\theta$ in equilibrium position.

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Non-inertial frame of reference (Train)
FBD of bob w.r.t train. (real forces + pseudo force):

with respect to train, bob is in equilibrium
$\therefore$ $\sum F_x=0\Rightarrow Tsin\theta =ma$ ..........(i)
$\therefore$ $\sum F_y=0\Rightarrow Tcos\theta =mg$ .........(ii)
From Eqs (i) and (ii), we get the result
$\theta =ta{n}^{-1}\frac{a}{g}$