A truck is stationary and has a bob suspended by a light string, in a frame attached to the truck. The truck suddenly moves to the right with an acceleration of a. The pendulum will tilt (a) to the left and angle of inclination of the pendulum with the vertical is tan ⁻¹(g/a) (b) to the left and angle of inclination of the pendulum with the vertical is sin ⁻¹(g/a) (c) to the left and angle of inclination of the pendulum with the vertical is tan ⁻¹(a/g) (d) to the left and angle of inclination of the pendulum with the vertical is sin ⁻¹(a/g)

Answer: (c). In the truck's frame, a pseudo force ma acts on the bob towards the left (opposite to a). In equilibrium: Tsin θ = ma, Tcos θ = mg tan θ = a/g, and the bob tilts to the left. So the answer is (c).

A truck is stationary and has a bob suspended by a light string, in a… | NEET 2019

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Equilibrium, Third Law & Frames

A truck is stationary and has a bob suspended by a light string, in a frame attached to the truck. The truck suddenly moves to the right with an acceleration of $a$ . The pendulum will tilt

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Answer: (c)

In the truck's frame, a pseudo force $ma$ acts on the bob towards the left (opposite to $a$ ).
In equilibrium: $T\sin\theta = ma$ , $T\cos\theta = mg$
$\tan\theta = \frac{a}{g}$ , and the bob tilts to the left.
So the answer is (c).

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