A man of mass 70 kg stands on a weighing scale in a lift which is moving (a) upwards with a uniform speed of 10 m s 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 ?

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

1.	A man of mass 70 kg stands on a weighing scale in a lift which is moving (a) upwards with a uniform speed of 10 m s 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 ?
Answer» Solution :MASSOF personm= 70kg (a )when itmovesin upwarddirectinwithconstantvelocity WEIGHT ofpersonrecorded in SPRINGBALANCE W= mg `=70 xx 10` `=700 N` Weighingscale will measure 70 kgweight (b )whenliftis movingdownwithaccelerationin upwarddirectionresultantdirection resultantaccelerationg= g- a Weight recorded mg = mg- ma `=70 (10-5)` `=350N` `: m = (mg )/( g ) = (350)/( 10)` Weighingscalewillmeasure35 kgweight (c ) Whenliftmoveswithupwardaccelerationwill be indownwarddirection Weight recordedin springbalance `:., mg = mg +ma` `=70 (10 + 5)` `70 xx 15` 1050 N `:.= (mg)/( g) = (1050)/( 10) = 105 kg` Weighingscalewillmeasure105 kgweight (d )whenliftis fallingfreelythenpseudoaccelerationwill beupwarddirection `:.`Weightrecorded w=mg `=m(0)` `=0` this iscalledweightlessness.