# Homework Help: Trajectory, Wind Resistance, and Acceleration

1. Oct 7, 2006

### Soaring Crane

Suppose the force of wind resistance is proportional to the speed of the object and in the direction opposite of the object’s velocity. If you throw an object upward, when is the magnitude of the acceleration the highest?

a.It is highest at the top of its trajectory.
b.It is the highest right after the object is released.
c.The acceleration of the object is the same throughout the entire trajectory.

I would think that it would be c. but I am unsure of the thought procee for this one. Can anyone give me advice or guide me through this one?

Thanks.

2. Oct 7, 2006

### neutrino

Think of the velocities the object has at each of the positions mentioned.

3. Oct 7, 2006

### arildno

Now let's look at this qualitatively:
1. When the object is moving UPWARD, then the vertical part of the air resistance add to that of the weight to create a downwards acceleration greater than gravity alone.
What is the case when the object is moving DOWNWARDS?

So, when would the object have the strongest vertical acceleration?

2. In the horizontal component, air resistance steadily retards the object.
So when would the object have the strongest horizontal acceleration?

3. What is then your conclusion?

4. Oct 7, 2006

### Soaring Crane

This is my attempt at applying what I just read from my posts. Hopefully, I absorbed something after rereading each line.

I was thinking of the velocity vector, but I still only half-understand air resistance. Wouldn't the horizontal component of velocity remain the same? In the vertical direction, wouldn't the initial velocity vector be greatest before the object reaches the top, so the acceleration would be greater when the object just starts to move or after it is released?

Thanks again.

5. Oct 7, 2006

### arildno

"Wouldn't the horizontal component of velocity remain the same?"

Nope!
Air resistance force is a vector quantity strictly anti-parallell to the object's velocity vector. Thus, if you start out with some horizontal velocity component, you will also experience a horizontal air resistance component in the opposite horizontal direction.

6. Oct 5, 2010

### preluderacer

I believe it is at its highest right after u throw right? Because air resistance + gravitiy?