A person of mass 50 kg stands on a weighing scale on a lift. If the lift is ascending upwards with a uniform acceleration of 9 

ms^-2, what would be the reading of the weighing scale? (Take g = 10 m s^-2) 

The reading on the scale is a measure of the force on the floor by the person. By the Newton's third law this is equal and opposite to the normal force N on the person by the floor. 

$\therefore$ When the lift is ascending upwards with a acceleration of 9 m s^-2, then 

$$\begin{gathered} \mathrm{N}-50\times 10=50\times 9 \mathrm{or} \\ \mathrm{N}=50\times 10+50\times 9 \\ =50(10+9) \\ =950 \mathrm{N} \end{gathered}$$

Therefore, reading of weighing machine is 95 kg.