Bullet fired in a pendulum. Calculate the initial speed of the bullet.

[febreze]

I've been trying to figure this out for a while and it's due tomorrow...any help would be greatly appreciated.

A .005 kg bullet is fired into a 4.0 kg pendulum bob initially at rest and becomes embedded in it. If the pendulum rises a vertical distance of 5.0 cm, calculate the initial speed of the bullet.

I tried to use a kinematics equation to find the velocity, but I needed an acceleration, so I tried to use F=ma, but I'm retarded or something but couldn't figure it out any way. Thanks for any help offered.

 

[ZapperZ]

I've been trying to figure this out for a while and it's due tomorrow...any help would be greatly appreciated.
A .005 kg bullet is fired into a 4.0 kg pendulum bob initially at rest and becomes embedded in it. If the pendulum rises a vertical distance of 5.0 cm, calculate the initial speed of the bullet.
I tried to use a kinematics equation to find the velocity, but I needed an acceleration, so I tried to use F=ma, but I'm retarded or something but couldn't figure it out any way. Thanks for any help offered.

1. Use conservation of momentum when the bullet hits the pendulum.

2. Then use conservation of energy when the bullet+pendulum swing to the top.

Zz.

 

[quicknote]

I would suggest using conservation of momentum to solve this problem. The initial momentum of the bullet will be equal to the final momentum of the pendulum-bullet system. The initial momentum of the bullet can be calculated using its mass and initial velocity, which is what we are trying to find. The final momentum of the system can be calculated using the mass of the pendulum-bullet system and its final velocity, which can be determined using the given information about the pendulum's rise.

Using the equation P=mv, we can set the initial momentum of the bullet equal to the final momentum of the system, and solve for the initial velocity of the bullet.

P_initial = P_final

m_bullet * v_initial = (m_bullet + m_pendulum) * v_final

Solving for v_initial, we get:

v_initial = (m_bullet + m_pendulum) * v_final / m_bullet

Plugging in the given values, we get:

v_initial = (0.005 kg + 4.0 kg) * (0 m/s) / 0.005 kg = 0 m/s

Therefore, the initial speed of the bullet is 0 m/s. This could be due to a number of factors, such as the bullet not being fired with enough force or frictional forces slowing it down. I would suggest double checking your calculations and also considering any other factors that may have affected the bullet's initial speed.