Question

a man of mass 75kg lifts an object of mass m to height of 5 m. then same object is lifted by a boy of mass 40 kg to same height.
if value of mass 'm' is 5 kg find the ratio of P.E possessed by man and boy.
(g=10)

Answer 1

$$\begin{gathered} \mathrm{Potential}\mathrm{energy}\mathrm{of}\mathrm{man}\left({\mathrm{PE}}_{\mathrm{man}}\right)=m\times g\times h=75\times 10\times (5m-m)=750\times 4m \\ \mathrm{Potential}\mathrm{energy}\mathrm{of}\mathrm{boy}\left({\mathrm{PE}}_{\mathrm{boy}}\right)=m\times g\times h=40\times 10\times (5m-m)=400\times 4m \\ \frac{\mathrm{Potential}\mathrm{energy}\mathrm{of}\mathrm{man}\left({\mathrm{PE}}_{\mathrm{man}}\right)}{\mathrm{Potential}\mathrm{energy}\mathrm{of}\mathrm{boy}\left({\mathrm{PE}}_{\mathrm{boy}}\right)}=\frac{750\times 4m}{400\times 4m}=\frac{15}{8} \end{gathered}$$