Answer: 2:1
Explanation:
Given
Mother has four times the mass of young son
If they possess same kinetic energy then [tex]K_m=K_s[/tex]
[tex]\Rightarrow K_m=\dfrac{1}{2}\times m_m\times v^2_m[/tex]
[tex]\Rightarrow K_s=\dfrac{1}{2}\times m_s\times v^2_s[/tex]
Equate the energy
[tex]\Rightarrow \dfrac{1}{2}\times m_m\times v^2_m=\dfrac{1}{2}\times m_s\times v^2_s\\\\\Rightarrow \dfrac{1}{2}\times 4m_s\times v^2_m=\dfrac{1}{2}\times m_s\times v^2_s\\\\\Rightarrow 4 v^2_m=v^2_s\\\\\Rightarrow \dfrac{v_s}{v_m}=\sqrt{4}\\\\\Rightarrow \dfrac{v_s}{v_m}=2[/tex]
Thus, the ratio of speed is 2:1.
