What is the magnitude of the upward force of friction

[kumar_23]

is it asking for initial velocity? this is a tough one!

 

[hage567]

No, it has given you the initial velocity. What you need to find is the new velocity after the force of the wind has acted on the wind sled.

 

[kumar_23]

how do we figure that out? i think a free body diagram will be helpful in problem.
then, do we have to break the two directions into components?

 

[hage567]

Well, you know the force acting. What do you need to find the new velocity? Think Newton's second law.

 

[hage567]

I don't think you need to break it up into components.

 

[kumar_23]

do you use fnet= ma? or do i need to find a?

 

[hage567]

do you use fnet= ma? or do i need to find a?

I'm not too sure what you mean by that, but yes, this is the equation you need. Make sure you understand what the equation means.
One way to figure out what you're supposed to do with it is look at the three variables in that equation, which is the one you don't already know?

 

[kumar_23]

is it fnet i need to figure out ? do i use "constant velocity of 12 m/s (E) divided by 3.0 s. " to find acceleration ? then i figure out fnet by using fnet=ma after i figure out my acceleration.

****i'm not sure if this is how it's supposed to be done?****

 

[hage567]

READ the question! Write the information you have down in the proper form with the proper units so you can see what you have available to you.
The question states:

"a gust of wind from the southwest exerts a constant force of 1.0 * 10to the power of 2 on its sails"

This is your net force. So try to think of what you don't know but need to solve this problem. (Hint: you can find it by Newton's second law, it's the only thing you don't know in that equation)

 

[kumar_23]

sorry, i didnt notice the constant force part of the question
now, that tells me that i need to find acceleration using fnet = ma.
Do i then use the acceleration equation a = change in velocity /time. Do i then find final velocity by rearranging the equation?

 

[hage567]

that tells me that i need to find acceleration using fnet = ma. That's right!
Do i then use the acceleration equation a = change in velocity /time. Do i then find final velocity by rearranging the equation?

Yes, that should work.

 

[kumar_23]

so I am correct for the first time!

 

[kumar_23]

one more thing, is the initial velocity 0 m/s or 12 m/s in the equation?

 

[hage567]

What does the question say?

"A 4.0*10 kg wind sled is gliding across a frozen lake with a constant velocity of 12 m/s (E)"

Doesn't look like a zero to me! It says it's moving at a constant velocity, so you assume that's the initial velocity.

 

[kumar_23]

:shy: oh...the light bulb just went on!

 

[kumar_23]

so basically the question is just asking for the final velocity after the force hits it!
um...i was just wondering where in Canada are you from exactly?

 

[hage567]

Well yes, but the proper thing to say would be "what is the final velocity after the force accelerates it for three seconds". You've got the idea though.

I have to leave now, but I think you've got it all figured out.

 

[kumar_23]

can u just tell me where you're from?

 

[hage567]

Ontario, Canada.

 

[kumar_23]

by the way i added you to my buddy list. Thanks so much for your help. i really appreciated it!

 

[hage567]

You're welcome.

 

[kumar_23]

where in ontario? because i live in ON as well. sorry about the nosiness. it's just nice to meet someone in the same province.