question_answer

A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the spring reads 49 N, when the lift is stationary. What will be the reading of the spring balance, if the lift moves downward with an acceleration of\[5\text{m}{{\text{s}}^{-2}}\].              

Answer:

                When the lift is stationary. The reaction of the spring is equal to weight of the bag. \[\therefore \]  \[R=mg=49N\] or \[m=\frac{49}{g}=\frac{49}{9.8}=5kg\] When the lift moves downward. The reaction is \[R'=m(g-a)=5(9.8-5)=\mathbf{24N}.\]