Question

For a ballistic pendulum lab;

Describe in words how you used conservation of momentum in this lab. You must also explain why you were able to use conservation of momentum for this part of the problem

Answer 1

In a ballistic pendulum, the bullet(mass m) has the initial momentum and just after the collision with the suspended wooden block(mass M), the block-bullet together has the final momentum.

So,during the collision initial momentum = final momentum

Or, m*v = (M+m)V

So, v= (M+m)V/m __________(A)

Now, after the collision, the height to which the block + bullet has rised is measured as h and then conservation of energy applied as 0.5(M+m)V^2 = (M+m)gh

So, velocity of block + bullet just after the collision is V= (2gh)^1/2

Using this in (A), v is then found and v= (M+m)*(2gh)^1/2 / m

This value of v is then verified with the directly found v.

So, the bullets momentum is first converted into momentum of bullet+block and then the kinetic energy of bullet+block is converted to its potential energy. This potential energy is then measured, which gives the value for initial velocity of block+bullet(just after colision) and then this velocity is used to find value of initial speed of the bullet. this speed is the verified with velocity found directly.

The bullet after being fired and till getting into the block, is free from any other force or impulse; so, momentum is conserved you were able to use conservation of momentum for this part of the problem .