A cart of mass 6.0 kg moves with a speed of 3.0 m/s towards a second stationary cart with a mass of 3.0 kg. The carts move on a frictionless surface and when the carts collide they stick together. What is the ratio of the initial kinetic energy of the two-cart system to the final kinetic energy of the two-cart system?

a. 2
b. 1.5
c. 2.5
d. 1.25
e. 3

Respuesta :

Answer:b

Explanation:

Given

mass of first cart [tex]m_1=6 kg[/tex]

mass of second cart [tex]m_2=3 kg[/tex]

velocity of first cart [tex]v_1=3 m/s[/tex]

conserving momentum

[tex]m_1v_1+m_2v_2=(m_1+m_2)v[/tex]

[tex]6\times 3+3\times 0=(9)\cdot v[/tex]

[tex]v=2 m/s[/tex]

Initial kinetic Energy [tex]K.E._1=\frac{1}{2}m_1v_1^2+\frac{1}{2}m_2v_2^2[/tex]

[tex]K.E._1=\frac{1}{2}\cdot 6\cdot 3^2+0[/tex]

[tex]K.E._1=27 J[/tex]

Final Kinetic Energy

[tex]K.E._2=\frac{1}{2}(m_1+m_2)v^2[/tex]

[tex]K.E._2=\frac{1}{2}(6+3)\cdot 2^2=18 J[/tex]

Ratio of initial Kinetic Energy to the Final Kinetic Energy

[tex]=\frac{27}{18}=1.5[/tex]

The ratio of the initial kinetic energy would be:

1.5

Kinetic energy

According to the question,

First cart's mass, m₁ = 6 kg

Second cart's mass, m₂ = 3 kg

First cart's velocity, v₁ = 3 m/s

By using Conserving momentum, we get

→ m₁v₁ + m₂v₂ = (m₁ + m₂)v

By substituting the values,

6 × 3 + 3 × 0 = 9 × v

           18 + 0 = 9v

                   v = [tex]\frac{18}{9}[/tex]

                      = 2 m/s

The Initial Kinetic energy will be:

→ K.E₁ = [tex]\frac{1}{2}[/tex]m₁v₁² +  m₂v₂²

          = [tex]\frac{1}{2}[/tex] × 6 × (3)² + 0

          = 27 J

The Final Kinetic energy will be:

→ K.E₂ = [tex]\frac{1}{2}[/tex] (m₁ + m₂) v²

          = [tex]\frac{1}{2}[/tex] (6 + 3) (2)²

          = 18 J

hence,

The ratio will be:

= [tex]\frac{27}{18}[/tex]

= 1.5

Thus the above answer is correct.  

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