# Help vectors year 1 Physics undergrad.

1. Sep 15, 2011

### Eats Dirt

1. The problem statement, all variables and given/known data

a weight fastened to a roof 35 degrees above the horizontal, the weight is directed downward, in order that the unit not crush the roof tiles the component perpendicular to the roof can not exceed 425 N, What is the maximum allowed weight of the unit?

2. Relevant equations

Cos ... etc

3. The attempt at a solution

OK so lets name the force straight down which i will call W
the force perpendicular to the horizontal plane is 425 N i will call that J

so we find that angle between vector W and B is 35 degrees. so i use cos(35)=W/J
Jcos(35)=W
which means the force down is 348 N which issss.... WRONG :( tips would be great i really dont understand this .

2. Sep 15, 2011

### Modulated

Draw a force diagram. You're basically on the right track but seem to have ended up with the "unit" weighing less than the perpendicular force it exerts on the roof! See if you can work out what's gone wrong.

3. Sep 15, 2011

### Darth Frodo

Remember Cos is adjacent / hypoteneus. You may want to check your workings again