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On a cold winter day, a penny (mass 2.50 g) and a nickel (mass 5.00 g) are lying on the smooth (frictionless) surface of a frozen lake. With your finger, you flick the penny toward the nickel with a speed of 2.35 m/s.A) The coins collide elastically; calculate both of their final speeds

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Answer:

0.78333 m/s in the opposite direction

1.566 m/s in the same direction

Explanation:

[tex]m_1[/tex] = Mass of penny = 0.0025 kg

[tex]m_2[/tex] = Mass of nickel = 0.005 kg

[tex]u_1[/tex] = Initial Velocity of penny = 2.35 m/s

[tex]u_2[/tex] = Initial Velocity of nickel = 0 m/s

[tex]v_1[/tex] = Final Velocity of penny

[tex]v_2[/tex] = Final Velocity of nickel

As momentum and Energy is conserved

[tex]m_{1}u_{1}+m_{2}u_{2}=m_{1}v_{1}+m_{2}v_{2}[/tex]

[tex]{\tfrac {1}{2}}m_{1}u_{1}^{2}+{\tfrac {1}{2}}m_{2}u_{2}^{2}={\tfrac {1}{2}}m_{1}v_{1}^{2}+{\tfrac {1}{2}}m_{2}v_{2}^{2}[/tex]

From the two equations we get

[tex]v_{1}=\frac{m_1-m_2}{m_1+m_2}u_{1}+\frac{2m_2}{m_1+m_2}u_2\\\Rightarrow v_1=\frac{0.0025-0.005}{0.0025+0.005}\times 2.35+\frac{2\times 0.5}{0.4005+0.5}\times 0\\\Rightarrow v_1=-0.78333\ m/s[/tex]

The final velocity of the penny is 0.78333 m/s in the opposite direction

[tex]v_{2}=\frac{2m_1}{m_1+m_2}u_{1}+\frac{m_2-m_1}{m_1+m_2}u_2\\\Rightarrow v_2=\frac{2\times 0.0025}{0.0025+0.005}\times 2.35+\frac{0.005-0.0025}{0.005+0.0025}\times 0\\\Rightarrow v_2=1.566\ m/s[/tex]

The final velocity of the nickel is 1.566 m/s in the same direction

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