Question

A boy of mass 40 kg climbs up the stairs and reaches the roof at a height 8 min 5 s. Calculate : the force of gravity acting on the boy, (ii) the work done by him against the force of gravity, (iii) the power spent by the boy. (Take g = 10 m s-2)​

Answer 1

$\sf{(i)\: Force\: of\: gravity\: acting\: on\: the\: boy = mg}$

$\sf{Force\: of\: gravity\: acting\: on\: the\: boy= 40\times 10}$

$\sf{Force\: of\: gravity\: acting\: on\: the\: boy= 400 N}$

$\sf{(ii)\:Work\: done\: by\: him=mgh}$

$\sf{Work\: done\: by\: him=40\times 10\times 0.08}$

$\sf{Work\: done\: by\: him= 32 J}$

$\sf{(iii)\:Power=\frac{Work}{Time}}$

$\sf{Power=\frac{32}{5}}$

$\sf{Power= 6.4 Watt}$

Answer 2

$\sf{(i)\: Force\: of\: gravity\: acting\: on\: the\: boy = mg}$

$\sf{Force\: of\: gravity\: acting\: on\: the\: boy= 40\times 10}$

$\sf{Force\: of\: gravity\: acting\: on\: the\: boy= 400 N}$

$\sf{(ii)\:Work\: done\: by\: him=mgh}$

$\sf{Work\: done\: by\: him=40\times 10\times 0.08}$

$\sf{Work\: done\: by\: him= 32 J}$

$\sf{(iii)\:Power=\frac{Work}{Time}}$

$\sf{Power=\frac{32}{5}}$

$\sf{Power= 6.4 Watt}$