# What is the bird's speed immediately after swallowing?

1. Nov 12, 2007

### cse63146

[SOLVED] Momentum Question

1. The problem statement, all variables and given/known data
A 300 g bird flying along at 6 m/s sees a 10 g insect heading straight toward it with a speed of 30 m/s (as measured by an observer on the ground, not by the bird). The bird opens its mouth wide and enjoys a nice lunch.

What is the bird's speed immediately after swallowing?

2. Relevant equations

$$p_{1}$$ = $$p_{2}$$

3. The attempt at a solution

I know relative speed is the sum of the bird's and bug's speed since they are headed in opposite direction, and 30 + 6 = 36 so

$$m_{bird}$$$$v_{bird}$$ + $$m_{bug}$$$$v_{bug}$$ = ($$m_{bird}$$ + $$m_{bug}$$)$$v_{final}$$
0.3(36) + 0.01(36) = (0.3 + 0.01)$$v_{f}$$

$$v_{f}$$ = (0.3(36) + 0.01(36))/0.31 = 34.87 m/s

but this is wrong, probably because the relative speed. Any suggestions? Thanks.

Last edited: Nov 12, 2007
2. Nov 12, 2007

### Math Jeans

Check the velocities that you entered.

3. Nov 12, 2007

### Vidatu

Its been a while since I did one like this, but I don't think yo should use the relative speed like that. You have the bird accelerating massively, which is impossible.

I'd say its more like (0.3kg)(6m/s)-(0.01kg)(30m/s)

4. Nov 12, 2007

### cse63146

I know something is wrong with them, the problem is I can't figure out what.

According to my assigment:

so that's what I thought it was, which apperantly isnt.

5. Nov 12, 2007

### tyco05

You're right..... it is wrong because of the relative speed.

Don't use relative speed. The bird has a velocity of 6m/s and the bug has a velocity of -30m/s

6. Nov 12, 2007

### tyco05

I'm assuming that the answer wants the bird's speed relative to the ground

7. Nov 12, 2007

### cse63146

God dammit...

I tried doing that earlier in the day using that method... now I relased I put the decimal in the wrong place... *sigh*

Thanks for the help, I would have been stuck on this for hours otherwise