(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

I am worried that I don't understand a basic part of figuring out the component forces in the following problem. I have a full worked example but there is a few steps which I don't understand why we use sin for the x component and not cos (understand why I am really worried as it appears to be basic trig :/)

A 58-kg skier is coasting down a 25° slope, as Figure 6.7a shows. Near the top of the slope, her speed is 3.6 m/s. She accelerates down the slope because of the gravitational force, even though a kinetic frictional force of magnitude 71 N opposes her motion. Ignoring air resistance, determine the speed at a point that is displaced 57 m downhill.

2. Relevant equations

vf = √2(KE_{f}) / m

= √(2(1/2 mv_{0}^{2}+ Sigma F cos theta s)/m

= √(2(1/2 mv_{0}^{2}+ mg sin 25 - fk s) /m

= √(2(1/2 mv_{0}^{2}+ 170N cos 0 x 57) / 58

= 19m/s

3. The attempt at a solution

This was in my textbook:

a free-body diagram for the skier and shows the three external forces acting on her: the gravitational force , the kinetic frictional force , and the normal force . The net external force along the y axis is zero, because there is no acceleration in that direction (the normal force balances the component mg cos 25° of the weight perpendicular to the slope). Using the data from the table of knowns and unknowns, we find that the net external force along the x axis is:

SigmaF = mg sin 25 - f_{k}

= (58)(9.8)(sin 25)(71)

= 170N

I look at sin and think we are looking at y component. I can't see why we would used sin for x component - can someone explain?

Many thanks

H

x

ps. please forgive formating - each time I use latex it just puts large gaps in the place of symbols :)

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Conceptual difficulty - Work

**Physics Forums | Science Articles, Homework Help, Discussion**