A bullet of mass 10g is fired horizontally to a block of wood of mass 3 kg that is at rest in which the bullet goes through the wood and travels with a speed of 250m/s and the wood moved for 5 m from its original position. The coefficient of friction between the ground and the wood is 0.2
a) What is the velocity of the bullet when it is fired?
I am not sure but Is this an inelastic collision? where you would use
m1v1i + m2v2i = m1v1f + m2v2f
if I call m1= bullet and m2= wood
we are looking for v1i? but we need to find v2f first right?
OR can this be a completely inelastic collision? but I don't think that is true since the problem did NOT state that the bullet sticks to the wood.
a) What is the velocity of the bullet when it is fired?
I am not sure but Is this an inelastic collision? where you would use
m1v1i + m2v2i = m1v1f + m2v2f
if I call m1= bullet and m2= wood
we are looking for v1i? but we need to find v2f first right?
OR can this be a completely inelastic collision? but I don't think that is true since the problem did NOT state that the bullet sticks to the wood.
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This is an inelastic collision, but not completely inelastic. Here's what I would do to solve it:
You know the mass of the block, so you can find its weight. The force that friction exerted on the block is 0.2 times the weight of the block. Friction exerted that force over a distance of 5m, so we can find the negative work that the friction did on the block by multiplying the frictional force by the distance it was exerted. The amount of negative work that friction did on the block would be how much kinetic energy the block gained from the bullet. We can find the kinetic energy of the bullet after the collision easily using 1/2mv^2. Add this kinetic energy to the kinetic energy that the block had before it was slowed down by friction. This addition will be equal to the kinetic energy of the bullet when it was fired.
You know the mass of the block, so you can find its weight. The force that friction exerted on the block is 0.2 times the weight of the block. Friction exerted that force over a distance of 5m, so we can find the negative work that the friction did on the block by multiplying the frictional force by the distance it was exerted. The amount of negative work that friction did on the block would be how much kinetic energy the block gained from the bullet. We can find the kinetic energy of the bullet after the collision easily using 1/2mv^2. Add this kinetic energy to the kinetic energy that the block had before it was slowed down by friction. This addition will be equal to the kinetic energy of the bullet when it was fired.