Question

A simple pendulum having a bob of mass m is suspended from the ceiling of a car used in a stunt film shooting. The car moves up along an inclined cliff at a speed v and makes a jump to leave the cliff and lands at some distance. Let R be the maximum height of the car from the top of the cliff. The tension in the string when the car is in air is

(a) mg

(b) mg - mv²/R

(c) mg + mv²/R

(d) zero.

Answer 1

(d)  zero.

Explanation:

During the jump of the car from the cliff its trajectory is like a projectile and from the maximum height it is freely falling under gravity with an acceleration g downward. Taking it as frame of reference, it is a non-inertial frame of reference. So a pseudo force equal to mg has to be applied to the bob in upward direction which neutralizes the weight and making it zero. So tension in the string is zero.