Ballistics pendulum - sort of - COM

In summary, a 4.00-g bullet with a velocity of 400 m/s is fired into a wooden block with a mass of 0.800 kg, causing the bullet to emerge with a speed of 120 m/s. The block slides a distance of 45.0 cm along the surface and we are asked to find the coefficient of kinetic friction, decrease in kinetic energy of the bullet, and the kinetic energy of the block after the bullet passes through it. Using W=Fs and F=ma, the answers obtained are: (i) 0.221996 for the coefficient of kinetic friction, (ii) 291.2J for the decrease in kinetic energy of the bullet, and
  • #1
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Homework Statement


A 4.00-g bullet, traveling horizontally with a velocity of magnitude 400 m/s, is fired into
a wooden block with mass 0.800 kg, initially at rest on a level surface. The bullet passes
through the block and emerges with its speed reduced to 120 m/s. The block slides a
distance of 45.0 cm along the surface from its initial position.
(i) What is the coefficient of kinetic friction between block and surface?
(ii) What is the decrease in kinetic energy of the bullet?
(iii)What is the kinetic energy of the block at the instant after the bullet passes through it?

We have a physics exam coming up and they gave us a couple of practice questions with no answers. I solved these but I am unsure if there correct can someone please take a look. thanks

i) 0.221996
ii) 291.2J
iii) 0.784J - i actually found this one while solving i) i used W=Fs i think you can use kinematics for acceleration and the use F=ma

Homework Equations





The Attempt at a Solution

 
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  • #2
'Got a little crazy with the precision in i), huh? :tongue: But seriously though, the answers look ok to me. :approve:
 
  • #3
yeah i guess i did. thanks
 

What is a ballistics pendulum?

A ballistics pendulum is a device used to measure the velocity of a projectile. It consists of a pendulum with a known mass and length, which is struck by the projectile and swings to a maximum height. By measuring the height of the swing, the initial velocity of the projectile can be calculated using the principle of conservation of momentum.

How does a ballistics pendulum work?

When a projectile strikes the pendulum, it transfers some of its momentum to the pendulum. This causes the pendulum to swing to a maximum height, which can be measured and used to calculate the initial velocity of the projectile. The pendulum acts as a temporary storage for the momentum of the projectile, allowing for an accurate measurement to be taken.

What is the center of mass (COM) and its role in a ballistics pendulum?

The center of mass (COM) is the point where the mass of an object is evenly distributed. In a ballistics pendulum, the COM is at the pivot point of the pendulum. This is important because the pendulum swings to its maximum height when the COM reaches its highest point, allowing for an accurate measurement of the initial velocity of the projectile.

What factors can affect the accuracy of a ballistics pendulum?

Several factors can affect the accuracy of a ballistics pendulum, including air resistance, friction at the pivot point, and the elasticity of the pendulum. Air resistance can slow down the swing of the pendulum, while friction can cause the pendulum to lose some of its energy. The elasticity of the pendulum can also affect the height of the swing, as a less elastic pendulum may absorb more of the projectile's energy.

What are the practical applications of a ballistics pendulum?

A ballistics pendulum has several practical applications, including in forensic science, where it can be used to determine the velocity of a bullet. It is also commonly used in physics experiments to demonstrate the principle of conservation of momentum. Additionally, the concept of a ballistics pendulum has been applied to other devices, such as the ballistic pendulum rocket, which uses the same principle to launch a rocket.

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