A 20-kg girl and a boy on ice skates stand at rest facing each other. They push each other as hard as they can, and the boy moves to the left with a velocity of 2 m/s, while the girl moves to the right with a velocity of 3 m/s. (a) What is the boy's mass?

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Answer 1 · 2018-05-09T08:20:54

${mass}_{boy} = 30 k g$ $"mass"_"boy"=30" "kg$

boy:

mass $= m k g$ $=m" "kg$

$u_{i} = 0 m s^{- 1}$ $u_i=0" "ms^(-1)$

$u_{f} = - 2 m s^{- 1}$ $u_f=-2" "ms^(-1)$

girl

mass $= 20 k g$ $=20" "kg$

$u_{i} = 0 m s^{- 1}$ $u_i=0" "ms^(-1)$

$u_{f} = 3 m s^{- 1}$ $u_f=3" "ms^(-1)$

initial momentum $=$ $=$ final momentum

$0 = - 2 m + 20 \times 3$ $0=-2m+20xx3$

$0 = - 2 m + 60$ $0=-2m+60$

$\Rightarrow m = 30$ $=>m=30$

$:. "mass"_"boy"=30" "kg$