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
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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

G1 Physics · Accepted Answer

Let the man's speed be v and the boy's speed be u. Initially ½Mv²=½(¼Mu²), so u=2v. After the man speeds up by 1 m/s, ½M(v+1)²=¼Mu²=Mv², hence (v+1)²=2v² and v=1+√2 m/s. Hence D.