A man weighs 70kg. He stands on a weighting machine in a lift, which is moving
A man weighs 70kg. He stands on a weighting machine in a lift, which is moving
(a) Upwards with a uniform speed of 10m/s.
(b) Downwards with a uniform acceleration of 5m/s2.
(c) Upwards with a uniform acceleration of 5m/s2. Take g = 9.8m/s2.
What would be the readings on the scales in each case what would be the reading if the lift mechanism failed and it came down freely under gravity?
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Here, m = 70kg, g = 9.8m/s2
(a) When the lift moves upwards with a uniform speed, its acceleration is zero.
R = mg = 70 x 9.8 = 686 N
(b) When the lift moves downwards with
a = 5m/s2
R = m (g – a) = 70(9.8 + 5) = 336N
(c) a = 5m/s2
R = m (g + a) = 70 (9.8 + 5) = 1036N
If the lift falls freely under gravity, a = g
R = m (g – a) = m (g – g) = 0
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