InterviewSolution
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InterviewSolution
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A man of mass 70 kg stands on a weighing machine in a lift, which is moving (a) upwards with a uniform speed of `10ms^(-1)` (b) downwards with a uniform acceleration of `5 ms^(-2)` (c) upwards with a uniform acceleration of `5 ms^(-2)` What would be the readings on the scale in each case ? (d) What would be the reading if the lift mechanism failed and it hurtled down freely under gravity ? |
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Answer» Here m = 70 kg , g `= 10 ms^(m/s^(2)` The weighting machine in each case measueres the reaction R i.e. the apparent weight. (a) When the lift moves upwards with a uniform speed, its acceleration is zero . R = mg = `70 xx 10 `= 700 N (b) When the lift moves downwards with a = 5 `ms^(-2)` R = `m(g - a) = 70( 10 - 5)` = 350 N (c ) When the lift moves upwards with a = `5ms^(-2)` R =` m(g + a) = 70 (10 + 5)` = 1050 N (d) If the lift were to come down freely under gravity , downward acc. a = g `therefore` R = m(g-a) = m(g-g)` = Zero. |
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