Q4.5 Work and kinetic energy I (S)

A 30 g bullet, initially travelling at 500 ms-1, penetrates 12 cm into a solid wall.
  1. Calculate the average work done by the wall in stopping the bullet.
  2. Assuming that the wall exerts a constant force on the bullet, calculate the magnitude of that force.
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Hint

What is the relationship between work and kinetic energy?
 

Solution

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Solution

  1. The work done by the wall is simply the change in kinetic energy of the bullet. The change in kinetic energy is negative; therefore so is the work done by the wall:

    -0.5×0.03×500×500=-3750 J

  2. If the force provided by the wall is constant, then the total work done by the wall in distance d is

    W=Fd

    With d=12 cm, the magnitude of the average force is 3750/0.12 = 31250 N