physics help

[pizza1994]

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A back-packer grabs her 75 Npack and drags it with a constant speed at an angle
of 30° to the horizontal. The force she applies to the pack is 40 N. What is the
magnitude ofthe kinetic frictional force that is acting on the pack?

for this question do we hvae to account for the fact that gravoty is mgsin(theta) or not?

how do we do this? Can someone please help me! really appreciate all the help 🙂

 

[pizza1994]

A back-packer grabs her 75 Npack and drags it with a constant speed at an angle
of 30° to the horizontal. The force she applies to the pack is 40 N. What is the
magnitude ofthe kinetic frictional force that is acting on the pack?

for this question do we hvae to account for the fact that gravoty is mgsin(theta) or not?

how do we do this? Can someone please help me! really appreciate all the help 🙂

ALSO THIS IS FROM BR BOOKS!!!!!!

 

[orangetea]

I would start by drawing a force diagram.
So you have your backpack and the forces acting on it are Gravity(pointing down), normal force( pointing up), Force of pull (you can draw that at an angle pointing up.
Now what you need to realize is that you are pulling the backpack at constant speed so there is no acceleration and so ma=0. It makes the problem easier because you can just put your forces equal to each other.

Force of pull cos(theta) = Normal force (Uk)
*notice that normal force= mg

40 cos(30)=75 (Uk)
*notice that it is cosine because you are pulling the backpack in the horizontal direction.

using this equation you can find the coefficient of kinetic friction. Once you have that you know that Force of friction= Normal force * Uk

Then you have your answer 🙂

There are a lot of concepts in this problem so I wouldn't necessarily memorize HOW to do it but more so why the math works out the way it does. I used to have a lot problem with these (and still do) but with practice it's gotten a lot better.