# Homework Help: What should I do next?

1. Nov 7, 2004

### pkhor

the original problem:
A 0.010-kg bullet traveling horizontally at 400.0 m/s strikes a 4.0-kg block of wood sitting at the edge of a table. The bullet is lodged into the wood. If the table height is 1.2 m, how far from the table does the block hit the floor?

this is what i did:

lets the mass of bullet = m2
the mass of block of wood = m1
velocity of the block of wood before the collision take place = v1
velocity of the bullet = v2
velocity of the block and bullet after the collision take place = vf
momenta of the block = p1
momenta of the bullet = p2

the momentum of block and bullet after collision equals the sum of momenta of the block and the bullet before the collision:

pf = pi

The initial momentum is the sum of the momenta of the block and bullet

pf = p1 + p2

Since the block is initially at rest, p1 = 0. Then

pf = p2
or
(m1 + m2)(vf) = (m2)(v2)

Solving for vf:

vf = [(0.010)(400.0)]/(4.0+0.010) = 0.9975 m/s

And I stuck here because I didn't know how to calculate the distance from the table to the point that the block hit the floor.
Am I have to use the projectile motion concept?
Your help would be highly appreciate.

2. Nov 7, 2004

### Leong

Yes, you have to use the projectile motion formulas.