Question

A meter scale of mass $400gm$ is lying horizontally on the floor. If it is to be held vertically with one end touching the floor, the work to be done is (Take $g=10m/s^2$):

• A. $6J$
• B. $4J$
• C. $40J$
• D. $2J$

Answer 1

Answer: (D)

$2J$

Initially, the scale is lying on zero potential line. Thus initial potential line $U_i=0$

Mass of the meter scale $m=400g=0.4kg$

Center of mass of the scale lies at its center i.e. $h=0.5$ m

Final potential energy of the scale $U_f=mgh$

$\therefore$ $U_f=0.4\times 10\times 0.5=2J$

Work done $W=U_f-U_i$

$\therefore$ $W=2-0=2J$