An object weighing 70 kg is kept in a lift. Find its weight as a recorded by a spring balance when the lift a) Moves upwards with a uniform velocity of ms-1 b) Moves upwards with a uniform acceleration of 2.2 ms-2 c) Moves downwards with a uniform acceleration of 2.8 ms-2 d) Falls freely under gravity
a) When the lift is moving upwards with a uniform velocity 5 ms-1, the reaction R or the pressure on the base is R = mg = 70 x 9.8 N = 686 N b) When lift is moving upwards with a uniform acceleration of 2.2 ms-2, the reaction R’ or the pressure on the bass increase and is given by R’ = m (g + a) = 70(9.8 + 2.2) N = 840 N c) When the lift descends with a uniform acceleration of 2.8 ms-2, the reaction R’’ is given by R’’ = m (g – a) = 70(9.8 – 2.8) N = 490 N d) When the lift falls freely under gravity , the reaction R’’’ is given by R’’’ = m (g – g) =0 The object appears to have become weightless.
