# Energy and basic math (proportionality)

**1. The problem statement, all variables and given/known data**

A person running in a race has to pick up a mass equal to her own mass. Assuming she can still do the same

amount of work, her speed will be changed by a factor of

a. 0.25

b. 0.50

c. 0.71

d. 1

e. 2

**2. Relevant equations**

E=1/2mv^{2}

**3. The attempt at a solution**

Since m is doubled, v^{2} should be halved. I’m stuck now. But the correct answer is 0.71. Can someone explain how?

http://ift.tt/1lUDO8a

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