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A 7.00 g bullet, when fired from a gun into a 1.10 kg block of wood held in a vise, penetrates the block to a depth of 9.60 cm. This block of wood is next placed on a frictionless horizontal surface, and a second 7.00 g bullet is fired from the gun into the block. To what depth will the bullet penetrate the block in this case

Respuesta :

Explanation:

The given data is as follows.

    Mass of bullet 1, [tex]m_{b}[/tex] = 7 g = [tex]7 \times 10^{-3} kg[/tex]

   Mass of block of wood, M = 1.10 kg

   Bullet penetrates to depth, [tex]x_{1}[/tex] = 9.60 cm = [tex]9.60 \times 10^{-2} m[/tex]

  Mass of bullet 2, [tex]m_{B}[/tex] = 7 g = [tex]7 \times 10^{-3} kg[/tex]

  Velocity of bullet = v

Let us assume that depth of penetration of the bullet is [tex]x_{2}[/tex].

According to the law of conservation of energy,

            Kinetic energy = Potential energy

        Kinetic energy = [tex]\frac{1}{2}mv^{2}[/tex]

and,       Potential energy = mgh

so, for bullet 1

           [tex]\frac{1}{2}m_{b}v^{2}_{1} = m_{b}gx_{1}[/tex] .......... (1)

For bullet 2,

     Kinetic energy of bullet 1 - kinetic energy of bullet 2 = Potential energy

 [tex]\frac{1}{2}m_{b}v^{2}_{1} - \frac{1}{2}(M + m_{b} + m_{B})v^{2}_{2} = m_{b}gx_{2}[/tex]

Using equation (1), we get

      [tex]m_{b}gx_{1} - \frac{1}{2}(M + m_{b} + m_{B})v^{2}_{2} = m_{b}gx_{2}[/tex]

        [tex]x_{2} = \frac{x_{1}(M + m_{b})}{(M + m_{b} + m_{B})}[/tex]

Putting the given values into the above formula as follows.

        [tex]x_{2} = \frac{x_{1}(M + m_{b})}{(M + m_{b} + m_{B})}[/tex]

                   = [tex]\frac{9.60 \times 10^{-2}(1.10 + 7 \times 10^{-3})}{(1.10 + 7 \times 10^{-3} + 7 \times 10^{-3})}[/tex]

                   = 0.0953 m

or,                = 9.53 cm    (as 1 m = 100 cm)

Thus, we can conclude that the bullet will penetrate at a depth of 9.53 cm.