+0

# Not doing too well at this one :/

0
224
2
+179

Hello.

I've been working at a 2D kinematics problem for a couple of days now, trying to work out how to do it:

you can view it here:

http://physics.stackexchange.com/questions/101508/finding-an-equation-to-solve-for-the-velocity-of-a-swimmer-crossing-a-river

I've worked out the idea of how to get the answer, however I just can't seem to get there.

I was hoping someone could explain how they went from step 1 to step 2. I can see some factoring going on but just can't quite work it out.

vest4R  Mar 23, 2017
Sort:

#1
+6913
0

Step 1: $$d_2\cdot v_s\cdot\cos 45^{\circ}=d_1\cdot(v_r-v_s\sin45^{\circ})$$

They multiplied out the bracket on the right hand side:

$$d_2\cdot v_s\cdot\cos 45^{\circ}=d_1\cdot v_r-d_1 \cdot v_s\sin45^{\circ}$$

and then they add d1 . vs sin45 each side:

$$d_2\cdot v_s\cdot\cos 45^{\circ}+d_1 \cdot v_s\sin45^{\circ}=d_1\cdot v_r$$

Factor out the common factor(vs):

$$v_s\cdot(d_2\cdot\cos 45^{\circ}+d_1\sin 45^{\circ})=d_1\cdot v_r$$ <-- Step 2!!

MaxWong  Mar 23, 2017

### 35 Online Users

We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners.  See details