Question

How fast should a man weighing $600N$ run so that his kinetic energy is $750J$? Take $g=10m{s}^{-2}$

• A. $10m{s}^{-1}$
• B. $5m{s}^{-1}$
• C. $15m{s}^{-1}$
• D. $20m{s}^{-1}$

Answer 1

Answer: (B)

$5m{s}^{-1}$

$W=600N,g=10m{s}^{-2},$ kinetic energy $=750J,v=?$

$W=mg$

$\therefore$ $600=m\times 10$

or, $m=60kg$

Now, kinetic energy$=\frac{1}{2}m{v}^2$

or, $750=\frac{1}{2}\times 60\times v^2$

or, $v^2=\frac{2\times 750}{60}=25$

or, $v=\sqrt{25}=5m{s}^{-1}$