A 50 g ball of clay traveling at speed vo hits and sticks to a 1.0 kg brick sitting at rest on a frictionless surface. a. Find an expression for the speed of the brick after the collision in terms of vo. b. What percentage of the mechanical energy is lost (i.e. converted to thermal energy) in this collision?

Respuesta :

To perform the procedure we proceed to define the equations that can help us,

So for the conservation of linear momentum we know that,

[tex]m1_u_1+m_2+u_2= (m_1+m_2)v[/tex]

Clearing for v,

[tex]v=\frac{m_1u_1+m_2u_2}{m_1+m_2}[/tex]

Substituting,

[tex]v= \frac{0.05Kg*v_0+1Kg(0m/s)}{0.05+1}[/tex]

[tex]v=0.0476v_0[/tex]

Where [tex]v_0[/tex] represents the initial velocity of the ball.

For the second part we need to know through kinetic energy the percentage loss, in this way

[tex](KE_i)\% = \frac{KE_{1i}-KE_{1f}}{KE_{1i}} *100[/tex]

Initial

[tex]KE_{1i}=\frac{1}{2}m_1u^2_1[/tex]

Final

[tex]KE_{1f}=\frac{1}{2}(m_1+m_2)v^2[/tex]

Substituting everything in the percentage equation we have

[tex](KE_i)\% = \frac{0.5*(0.05*v_0^2-0.5(0.05+1))*0.0476v_0}{0.5(0.05)*v_0^2}*100[/tex]

[tex](KE_i)\% = \frac{0.05*v_0^2-0.002379*v_0^2}{0.05*v_0^2}*100[/tex]

[tex](KE_i)\% = 95.2\%[/tex]

Which means that this is the percentage of loss of kinetic energy.

The speed of the brick after the collision is 0.048v₀.

The percentage of the mechanical energy lost in the collision is 95.2%.

The given parameters;

  • mass of the ball, m₁ = 50 g = 0.05 kg
  • speed of the ball, = v₀
  • mass of the brick, m₂ = 1 kg

Let the speed of the brick after collision = v

Apply the principle of conservation of linear momentum;

[tex]m_1v_0 + m_2 u_2 = v(m_1 + m_2)\\\\0.05v_0 + 0 = v(1 + 0.05)\\\\0.05v_0 = 1.05v\\\\v= \frac{0.05v_0}{1.05} \\\\v = 0.048 v_0[/tex]

Thus, the speed of the brick after the collision is 0.048v₀

The total initial kinetic energy;

[tex]K.E_i = \frac{1}{2} \times 0.05 \times v_0^2 \ + \ \frac{1}{2} \times 0.05 \times 0^2\\\\K.E_i = 0.025v_0^2[/tex]

The total final kinetic energy;

[tex]K.E_f = \frac{1}{2} \times (1.05) \times (0.048v_0)^2\\\\K.E_f = 0.0012 v_0^2[/tex]

The percentage of mechanical energy lost during the collision;

[tex]= \frac{0.025v_0^2 \ - \ 0.0012v_0^2}{0.025v_0^2} \times 100\%\\\\= 95.2 \ \%[/tex]

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