Question

A man of mass 70kg stands on a weighing scale in a lift which is moving

1. upwards with a uniform speed of 10ms^-1

2. downwards with a uniform acceleration of 5ms^-2

3. upwards with a uniform acceleration of 5ms^-2 What would be the readings on the scale in each case?

4. What would be the reading if the lift mechanism failed and it hurtled down freely under gravity?

Answer 1

1. a = 0, R = mg = 70 × 10 N = 700N

2. mg – R = , ma ; R – mg – ma = (g – a)

= 70(10 – 5) N = 350N

3. R – mg = ma or R = m(g + a)

= 70(10 + 5)N = 1056 N

4. In the event of free fall, it is a condition of weight lessness.