Question about a 2 dimensional motion question

[kevinf]

Homework Statement

At one instant a bicyclist is 35 m due east of a park's flagpole, going due south with a speed of 9 m/s. Then, 21 s later, the cyclist is 30 m due north of the flagpole, going due east with a speed of 15 m/s. For the cyclist in this 21 s interval, find each of the following.

Homework Equations

The Attempt at a Solution

first of all, i don't even understand the question. it says 35m due east then it says due south with a speed of 9m/s. can anyone please clarify the problem for me

 

[learningphysics]

That means his position is 35m east of the flagpole. But his velocity is 9m/s southbound...

 

[kevinf]

what does it mean by 9m/s south bound

 

[learningphysics]

what does it mean by 9m/s south bound

Means the direction he's traveling is south... downwards...

 

[kevinf]

yeah but the postion is east though, that's what doesn't make sense to me. so is it south east

 

[learningphysics]

yeah but the postion is east though, that's what doesn't make sense to me. so is it south east

position and velocity are two separate things... a person can be located anywhere and still be traveling in the south direction... ie downwards... at that particular moment he's located east of the flagpole... in while after he's traveled south a little more he won't be directly east of the flagpole... he'll be south east...

But at that particular moment he is east of the flagpole... and his instantaneous velocity is south...

 

[kevinf]

so he goes 35 m east and then 9 m/s south?

 

[learningphysics]

so he goes 35 m east and then 9 m/s south?

No his location is 35m east of the flagpole... we don't know how he got there. he's traveling at a speed of 9m/s in the south-direction.

Draw a picture. I think you're making it more complicated that it needs to be...

 

[kevinf]

ok i get the first part but how does he end up north of the flag pole later on

 

[learningphysics]

ok i get the first part but how does he end up north of the flag pole later on

we don't know... anything could have happened in those 21s... what does the question ask you to find?

 

[kevinf]

it asks for the average acceleration, velocity, and displacement and the magnitude and direction of each

 

[learningphysics]

it asks for the average acceleration, velocity, and displacement and the magnitude and direction of each

ok. try calculating them... start with displacement...

 

[kevinf]

so would this be the right picture and the redline is the displacement?

 

[learningphysics]

so would this be the right picture and the redline is the displacement?

can't see the picture yet... might be a good idea to post on some image sharing site...

you can try this one:

http://www.imagevimage.com/

 

[kevinf]

http://www.imagevimage.com/images/Untitled.jpg

 

[learningphysics]

http://www.imagevimage.com/images/Untitled.jpg

that's not right. you're making it more complicated than it is... just start with displacement... ignore velocity for now...

The initial position is 35m east of the flagpole. The final position is 30m north of the flagpole. What is the displacement?

You should just have a line/arrow from the point 35m east of the flagpole, to the point 30m north of the flagpole.

What is the magnitude of this line? What is the direction?

 

[kevinf]

i understand the problem. thanks.