Задача id12684

A mathematical pendulum, i.e. a small ball on a thin thread, the mass of which can be neglected, is initially in a horizontal position. The length of the pendulum thread is l. At a distance l/2 below the suspension point of the pendulum there is a horizontal steel plate. To what height will the ball rise after hitting the plate, if the impact is considered absolutely elastic (Fig. 39)?

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