Question

A running boy has the samr kinetic energy as that of a man of twice his mass. If the speed of the boy is 14.14m/s, find the speed of the man?​

Answer 1

KE of boy =KE of Man

Mass of Boy = M

Mass of Man =2M

Speed of boy =14.14

Speed of Man =v

We know that

Kinetic Energy is given by

$k = \frac{1}{2} mv {}^{2}$

hence kinetic energy of boy

$ke_{boy} = \frac{1}{2} m(14.14) {}^{2}$

ke of man

$ke _{man} = \frac{1}{2} 2m \times v {}^{2}$

but

kinetic energy of boy =kinetic energy of Man

hence

$\frac{1}{2} m \times 200 = mv {}^{2}$

$100 = v {}^{2}$

$v = 10ms {}^{ - 1}$