- #1

9danny

- 10

- 0

**eng physics - help needed!!**

I have three simple problems that - even though I understand - I can't get the answer the book is saying...

1) Two forces with same magnitude F. What is the angle between the vectors if their sum has a magnitude of (sqrt)2F.

** ok - I'm doing R = (sqrt)2F therefore R = (sqrt)(Fx^2 + Fy^2) but Fx = Fy

Then R = sqrt(2F^2)

solving for F --> F= R/2 --> F= (sqrt2)/2

I'm doing (angle) = cos^-1 {[(sqrt2)/2]/[sqrt2]} but I get 60!! Book is telling me it should be 90deg... **

2) Two horses pull horizontally on ropes attached to a tree stump. The two forces F1 and F2 are such that the net force R has a magnitude equal to that of F1 and makes an angle of 90 with F1. Let F1=1300N. Find the magnitude of F2 and its direction.

** The book is answering 1840N and 135 deg. I broke R into Rx and Ry, same for F1...

Rx=(1300N)cos90 = 0 Ry=(1300N)sin90=1300 etc

Then using both components for both forces F1 and R - using Rx = F1x + F2x and solving for F2x (and F2y later) and again Pitagoreas' theorem I got ::

F2 = sqrt[ F2x^2 + F2y^2 ]

which - strange - gives me zero!! What did I do wrong? **