Question

An object weighing 60 kg is kept in a lift . Find its weight as a recorded by a spring balance when lift
(a) Moves upward with a uniform velocity of 2 m/s
(b) Moves upward with a uniform acceleration of 2.2 m/s²
(c) Moves downward with a uniform acceleration of 2.8 m/s²
(d) Falls freely under gravity .

Answer 1

$$\begin{gathered} \left(a\right) \\ \mathrm{W}\text{'}=\mathrm{m}\left(\mathrm{a}+\mathrm{g}\right) \\ =\mathrm{m}\left(0+\mathrm{g}\right) \\ =\mathrm{mg} \\ =60\times 9.8 \\ =588\mathrm{N} \\ \left(\mathrm{b}\right) \\ \mathrm{W}\text{'}=\mathrm{m}\left(\mathrm{a}+\mathrm{g}\right) \\ =\mathrm{m}\left(2.2+9.8\right) \\ =12\mathrm{m} \\ =12\times 60 \\ =720\mathrm{N} \\ \left(\mathrm{c}\right) \\ \mathrm{W}\text{'}=\mathrm{m}\left(\mathrm{g}-\mathrm{a}\right) \\ =\mathrm{m}\left(9.8-2.2\right) \\ =7.6\mathrm{m} \\ =7.6\times 60 \\ =456\mathrm{N} \\ \left(\mathrm{d}\right) \\ \mathrm{W}\text{'}=\mathrm{m}\left(\mathrm{g}-\mathrm{a}\right) \\ =\mathrm{m}\left(\mathrm{g}-\mathrm{g}\right) \\ =0 \end{gathered}$$