Statement I: A ball hung by a cord inside a car hangs vertically when the car moves with constant velocity, swings backward and settles at an angle when the car accelerates forward, and swings forward

Question

Statement I: A ball hung by a cord inside a car hangs vertically when the car moves with constant velocity, swings backward and settles at an angle when the car accelerates forward, and swings forward when the car brakes. Statement II: If the car accelerates up an incline with acceleration g sin θ , the cord hangs perpendicular to the inclined surface.

TestHub · Accepted Answer

Constant velocity is equivalent to rest, so the cord is vertical;

forward acceleration tilts it back by $tan^{- 1} (a / g)$ .

With

$a = g sin θ$

up the incline, the effective gravity in the car frame points normal to the plane, so the cord is perpendicular to the incline.

Both statements are true.

Option A.

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