# Physics question involving vectors and force (from Calc II)

• Sooneroo

## Homework Statement

A ball rests on a straight track aligned in the direction <x,y,z> . The ball will remain stationary unless it experiences a force of at least 120 N along the direction of the track. If a wind is blowing in the direction <a,b,c> , what is the magnitude of the wind's force required to move the ball, and in which direction will the ball move?

## Homework Equations

What is the magnitude of the wind's force required to move the ball, and in which direction will the ball move?

## The Attempt at a Solution

I'm not really sure how I should approach this, I managed to get the angle between these two vectors (using dot product) and try to use trig functions to get the x, y, z components of the force and equate that to 120 N. I'm not too sure though.

Any hints to get me started?

[I took off the points and replaced them with variables deliberately]

First, this really ought to be in the physics subsection of the homework and coursework, not the calculus subsection.

Second, note that ##\left|\mathrm{proj}_{\vec{u}}\left(\vec{v}\right)\right|=\dfrac{\vec{u}\cdot\vec{v}}{\left|\vec{u}\right|}##.

Yep, probably, but since we're here...

What exactly does projection mean? I know that's the equation for it, but how does it relate to the question?

Thanks.