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?

1 Answer
May 9, 2018

"mass"_"boy"=30" "kg

Explanation:

this is a conservation of momentum question

boy:

mass=m" "kg

u_i=0" "ms^(-1)

u_f=-2" "ms^(-1)

girl

mass=20" "kg

u_i=0" "ms^(-1)

u_f=3" "ms^(-1)

initial momentum=final momentum

0=-2m+20xx3

0=-2m+60

=>m=30

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