Question

as I was standing on a weighing machine inside a lift is recorded 50 kg weight suddenly for few seconds it record 45 kg weight what must have happened during that time explain with complete numerical analysis​

Answer 1

Answer:

When weight goes to 45N that means there is some acceleration; which means lift is going downwards

Explanation:

Let us say you start accelerating down from top floor of a building. The forces that are in play are - one, the gravitational force on you (mg) in downward direction and the push of the elevator floor on you in upward direction (let us call this “W”). If the elevator was stationery, this downward force mg and upward force by the floor would have been equal (hence no acceleration).

However, the fact that there is acceleration in downward direction means there is a net downward force and this is the absolute value of difference between W and mg. If we take any vector pointing in downward direction as negative and upward as positive and plug all forces in Newton’s 2nd law of motion equation

F net = ma, what we get is

W-mg = m(-a)

(a is negative since it is in downward direction)

W = m (g-a)………..(1)

This is the net force;

When lift is stationary, a = 0, W = 50N

Now, in eq 1, m and g are constant, so if the W goes to 45N that means there is some acceleration; which means lift is going downwards

Answer 2

Answer:

Given:

Initially the weight machine was recording 50 kgwt. But suddenly, it weighed 45 kgwt for a few seconds.

To find:

What happened in those few seconds ?

Concept:

The weight machine actually records the Normal Reaction force. In stationary conditions, it records the weight of the body because it's in a inertial reference frame and there is no acceleration.

But when it measures 45 kgwt, it means that the normal Reaction must have been decreased . This is possible if the lift is moving downwards with an Acceleration.

Mathematical Analysis:

In stationary conditions :

mg = 50 kgwt .

In moving down conditions :

mg - F = 45 kgwt

=> 50 - F = 45 kgwt

=> F = 5 kgwt.

So the body has experienced an pseudo-force of 5 kgwt upwards because of which the recording on the machine became 45 kgwt.

If you still have doubt in this answer, pls contact me at my inbox.