Question

A body of mass $7\text{kg}$ is projected vertically upwards from point $D$ at bottom of the tower to point $A$ at top of the tower of height $100\text{m}$. Find the difference in potential energy between point $A$ and point $D$ respectively. (Take $g=10{\text{m/s}}^2)$

• A. $700\text{J}$
• B. $7000\text{J}$
  
• C. $500\text{J}$
• D. $5000\text{J}$

Answer 1

The correct option is B $7000\text{J}$


It is given that mass of the body $m=7\text{kg}$, height of the tower $H=100\text{m}$, and $g=10{\text{m/s}}^2$

$U_A$ = Potential energy at point $A$ ( i.e top of the tower)

$U_D$ = Potential energy at point $D$ (i.e bottom of the tower)

At the reference line $H=0\therefore U_D=0$
Difference of potential energy between $A$ and $D$ is $\Delta U,U_A>U_D$

$\therefore \Delta U=U_A-U_D$

$\therefore \Delta U$$=mgH-mg\times 0=mgH=7\times 10\times 100=7000\text{J}$