Question

A boy can lift a maximum load of 250 N, of water: How many liters of mercury (density 13600 kg m-3) can he lift if contained in an identical vessel?

Answer 1

Volume of water= 1kg/m³
Mass of water being lifted⇒ Weight= Mass·acceleration
                                         ⇒ Mass= Weight÷acceleration     
                                         ⇒             250N÷ 10m/s²
                                         ⇒             25 Kg
Mass of water= 25 Kg in 25 litres (∴ 1kg water= 1litre water)
Boy can lift only 25Kg of any substance. (when g= 10m/s)
                      
Now mass of 1 litre of mercury= 13600 Kg per litre (∴ 1 m³= 1 litre)
 
 We will find how much litres of mercury weighs 25kg:

 Volume of mercury the boy can lift  = (25*1)/13600         =0.00183823529411764705882352941176 litres
or   

1.83 * 10⁻³ litres of mercury he can lift.