# A weighing machine installed in a lift. What will happen to the machine reading if lift starts accelerating downward?

30 views

John is standing on a weighing machine installed in a lift. The weighing machine shows the reading 50 kg when the lift is at rest.

What will happen to the reading of the machine if the lift starts accelerating downward?

posted Nov 24, 2017

The weighing machine converts force (Newton) exerted by the man into a number that is mass (kg) assuming acceleration due to gravity = (g) = 9.81 (m/s^2).
At rest the weighing machine experiences 50 × 9.81 = 490.5 N
This is then divided by 9.81 to get 50kg
When the lift accelerates downward with an acceleration 'a' the floor of the lift will not be able to give an equal and opposite reaction to the weight of the man. This reaction is what the scale relies on to get the reading, which is true when the ground and the person is stationary. Therefore the new weight in terms of force = 50 × (9.81 - a) N
so the weighing machine will indicate 50 × (9.81 - a)/9.81 kg as the new weight which is less than 50 kg or = 0 kg when a = 9.81 = g (When the lift is free falling).

Similar Puzzles

Two blocks A and B are tied with strings under water, as shown. The density of A is greater than water whereas that of B is less than water. The tensions in the strings are T1 and T2 respectively.

How will the tensions change if the whole setup starts accelerating in the upward direction?

+1 vote

A Van with all the windows closed contains some helium-filled ballons floating in it. When it starts accelerating what happens to balloons?

+1 vote

In a fruit store there was a unique weighing machine which was made to weigh only cherries and strawberries as they were priced the same.

Other fruits like water melons or mango had different machines as they were expensive.

A man successfully buys water melons at the price of cherries. How ?