# Physics Help

• Oct 6th 2012, 11:38 AM
Louisana1
Physics Help
A migrating bird is initially flying south at 7 m/s. To avoid hitting a high-rise building, the bird veers and changes its velocity to 6 m/s east over a period of 2 s. What is the bird's average acceleration (magnitude and direction) during this 2 s interval?
• Oct 6th 2012, 01:37 PM
ILikeSerena
Re: Physics Help
Quote:

Originally Posted by Louisana1
A migrating bird is initially flying south at 7 m/s. To avoid hitting a high-rise building, the bird veers and changes its velocity to 6 m/s east over a period of 2 s. What is the bird's average acceleration (magnitude and direction) during this 2 s interval?

Hi Louisana1!

Can you write the initial velocity as a vector?
And the final velocity as a vector as well?

If so, can you fill them in the formula for average accelation?
That formula is:
$\displaystyle \vec a_{average} = {1 \over \Delta t} (\vec v_{final} - \vec v_{initial})$
• Oct 6th 2012, 04:18 PM
Louisana1
Re: Physics Help
-1/2
• Oct 6th 2012, 04:52 PM
skeeter
Re: Physics Help
subtracting vectors ...

$\displaystyle i$ = unit vector in positive x-direction (East)

$\displaystyle j$ = unit vector in positive y-direction (North)

$\displaystyle v_0 = -7j$

$\displaystyle v_f = 6i$

$\displaystyle \Delta v = v_f - v_0 = 6i + 7j$

$\displaystyle a = \frac{\Delta v}{\Delta t} = \frac{6i + 7j}{2} = 3i +3.5j$

$\displaystyle |a| = \sqrt{3^2 + 3.5^2} = 4.6 \, m/s^2$

direction of the average acceleration vector ...

$\displaystyle \theta = \arctan\left(\frac{3.5}{3}\right) = 49^\circ$
• Oct 6th 2012, 06:05 PM
Louisana1
Re: Physics Help
not sure how you got the 49
Thanks skeeter
• Oct 6th 2012, 06:06 PM
skeeter
Re: Physics Help
the inverse tangent function on my calculator ...
• Oct 6th 2012, 06:07 PM
Louisana1
Re: Physics Help
It said it was wrong on my online homework
• Oct 6th 2012, 06:13 PM
skeeter
Re: Physics Help
Quote:

Originally Posted by Louisana1
It said it was wrong on my online homework

the angle is rounded to the nearest degree ... what is the criteria for entering answers as far as decimal places? If it's significant figures, it should be 50 degrees.
• Oct 6th 2012, 06:16 PM
Louisana1
Re: Physics Help
still wrong I'm trying to figure it out too
• Oct 6th 2012, 06:34 PM
HallsofIvy
Re: Physics Help
What was wrong? What answer did you give?
• Oct 8th 2012, 04:37 PM
Louisana1
Re: Physics Help
the 49 degrees is incorrect the other part is right