$A$ man who is running has half the kinetic energy of the boy of half his mass. The man speeds up by $1 \, m/s$ and then has the same kinetic energy as the boy. The original speed of the man was
$A$ man who is running has half the kinetic energy of the boy of half his mass. The man speeds up by $1 \, m/s$ and then has the same kinetic energy as the boy. The original speed of the man was
- A
$\sqrt 2 \,m/s$
- B
$( \sqrt 2 - 1)\,m/s$
- C
$2\, m/s$
- D
$(\sqrt 2 + 1)\, m/s$
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