# Um, how does this make sense?

1. Sep 19, 2004

### KaneOris

Hey guys, im a new member here and i dont know that much about physics so if this seems really obvious to you sorry, im only 15!

Ohk heres my problem.
I was looking at some stuff on impact
Now impact is reliant on impulse yes?
Now if I(impluse) = F average * change in time
And impulse is = momentum
momentum is Mass * Acceleration, or delta v / delta t
So if a bird is travelling at a velocity of 10m/s with a mass of 10kg but has no acceleration and it collides with an aeroplane which is travelling at 80m/s with a mass of 12 tons with no acceleration does that mean there is no impact as there is no acceleration?

2. Sep 19, 2004

### Tide

When they collide each object undergoes acceleration - the bird moreso than the airplane! :-)

3. Sep 19, 2004

### KaneOris

Oh i see, it all makes sense now thnx

4. Sep 19, 2004

### KaneOris

oh im an idiot i see now, p = mv, not ma, ma is f... oh well i feel dumb now, should probably get my formulae right first

5. Sep 20, 2004

### Staff: Mentor

incorrect signs

Not exactly. The net change in momentum is zero, so:
$$m_1(V'_1-V_1)= -m_2(V'_2-V_2)$$
Again, your signs are incorrect. If the collision is elastic (certainly not the case for the bird hitting the plane!) then KE is conserved, so:
$$m_1V'_1^2 + m_2V'_2^2 = m_1V_1^2 + m_2V_2^2$$