A man of mass 60 kg is standing in a lift at rest. What will be the reaction force on the man when the lift is (i) stationary, (ii) moving up with an acceleration of 4.9 m cdot s^(-2) , (iii) moving up at a constant speed, and (iv) moving up with a retardation of 4.9 mcdot s^(2)? [ g = 9.8 mcdot s^(2)]

A man of mass 60 kg is standing in a lift at rest. What will be the re

1.	A man of mass 60 kg is standing in a lift at rest. What will be the reaction force on the man when the lift is (i) stationary, (ii) moving up with an acceleration of 4.9 m cdot s^(-2) , (iii) moving up at a constant speed, and (iv) moving up with a retardation of 4.9 mcdot s^(2)? [ g = 9.8 mcdot s^(2)]
Answer» Solution :Reaction of the LIFT floor when the lift is stationary, R = mg = `60 xx 9.8 N ` = 588 N. (ii) The lift is moving up with an acceleration, a = 4.9 m`cdot s^(2)`. Reaction, R = m(g + a) = 60(9.8 + 4.9) N =882 N. (iii)When the lift is moving up at a constant speed, a = 0 . `therefore"" R = "mg" = 60 xx 9.8 N = 588` N. (iv) When the lift MOVES up with a retardation of 4.9 m`cdot s^(-2)`, R = m[g + (-a)] = m(g - a) = 60(9.8 - 4.9) N = 294 N.