Question

A person of mass $60kg$ wants to lose $5kg$ by going up and down a $10m$ high stairs. Assume he burns twice as much fat while going up than coming down. If $1kg$ of fat is burnt on expending $7000$ kilo calories, how many times must he go up and down to reduce his weight by $5kg$?

Answer 1

Energy produced by $1kg$ fat $=7000kcal$
Energy produced by $5kg$ fat $=5\times 7000kcal=35000Kcal$.
$=35\times {10}^{6}cal$
Energy consumed to go up onetime $=mgh$
Energy consumed to come down one time $=\frac{1}{2}mgh$ (given)
$\therefore$ Energy consumed to go up and down one time $=mgh+\frac{1}{2}mgh$
$E=\frac{3}{2}mgh=\frac{3}{2}\times 60\times 10\times 10=9000J$
Energy consume $1time=\frac{9000}{4.2}cal$.
Let he go up and down $n$ time to consumed energy $35\times {10}^{6}cal$
$n\times \frac{9000}{4.2}=35\times {10}^6$
$n=\frac{35\times 1000\times 1000\times 42}{9000\times 10}=\frac{3500}{3}\times 14$
$=\frac{49000}{3}=16.3\times {10}^{3}times$.