Is the lift moving upwards or downwards?

Classical Mechanics Level 2

A person of mass 40 kg stands on a weighing machine kept in a moving lift. The reading on the weighing machine is 200 $N$ . Is the lift accelerating upwards or downwards? (Take g to be $9.8 m/s^2$ )

Moving in any direction but with a uniform velocity Upwards Downwards

2 solutions

Ben Champion
Mar 26, 2016

The lift is ACCELERATING downwards. It could be moving up or down. As long as it is accelerating in the negative direction, the apparent weight will be less than the actual weight. Also, it doesn't really matter if its acceleration is less than 9.8 m/s^2. If it had an upward acceleration of 8 m/s^2 the apparent weight would be greater than the actual weight, and if it had a downward acceleration of 8 m/s^2 the apparent weight would be less than the actual weight.

Absolutely Correct.

Abhiram Rao - 5 years, 2 months ago

So shouldn't the question say "Is the lift accelerating upwards or downwards?" Seeing as how it could be moving in any direction as long as it is accelerating down, I'm not sure I understand why it asks which way it is moving.

Ben Champion - 5 years, 2 months ago

Abhiram Rao
Mar 26, 2016

Given , The apparent weight is 200 Newtons . The actual weight = $mass*g$ = $40*9.8$ or $40*10$ = 392 Newtons or 400 Newtons . So, as the actual weight is greater than the apparent weight , the lift moves with an acceleration less than 9.8 or 10 m/s^2 which is possible only when the lift moves downwards.

Is the lift moving upwards or downwards?

2 solutions

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