# A ball weighing 400 g is suspended by a weightless thread from the elevator ceiling.

A ball weighing 400 g is suspended by a weightless thread from the elevator ceiling. Is the thread tension more than 4 N when the lift is …?

Given:

m = 400 grams = 0.4 kilograms – the mass of the ball suspended on a weightless thread to the elevator ceiling;

g = 10 m / s ^ 2 – acceleration of gravity;

T = 4 Newtons – thread tension force.

It is required to determine the nature of the movement of the elevator with a thread tension greater than T.

If the elevator is at rest, then the tension force of the thread will be equal to:

T = m * g = 0.4 * 10 = 4 Newtons.

If the elevator moves upward with some acceleration a, then:

T – m * g = m * a;

T = m * g + m * a = 0.4 * 10 + 0.4 * a = 4 + 0.4 * a.

In this case, the thread tension will exceed 4 Newtons.

Answer: if the elevator moves upward with some acceleration.

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