Answer:
11m
3000000 m/s
Explanation:
[tex]m_1[/tex] = Mass of proton
[tex]m_2[/tex] = Mass of unknown element
[tex]u_1[/tex] = Velocity of proton = [tex]1.8\times 10^7\ m/s[/tex]
[tex]u_2[/tex] = Velocity of rebound = [tex]1.5\times 10^7\ m/s[/tex]
As the energy of the system is conserved we have
[tex]m_2=\dfrac{u_1-v_1}{u_1+v_1}m_1\\\Rightarrow m_2=\dfrac{1.8\times 10^7-(-1.5\times 10^7)}{1.8\times 10^7+(-1.5\times 10^7)}\times m_1\\\Rightarrow m_2=11m_1[/tex]
Mass of the unknown element is 11m
As the momentum of the system is conserved
[tex]m_1u_1=m_1v_1+m_2v_2\\\Rightarrow v_2=\dfrac{m_1(u_1-v_1)}{m_2}\\\Rightarrow v_2=\dfrac{m_1(1.8\times 10^7-(-1.5\times 10^7))}{11m_1}\\\Rightarrow v_2=3000000\ m/s[/tex]
The speed of the unknown nucleus immediately after such a collision is 3000000 m/s