# Homework Help: Force Vector into a Force (Power)

1. Oct 14, 2008

### Havok23

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

Find the power input of a force vector F acting on a particle that moves with a velocity vector v for each of the following situations.
(a) vector F = 4 N i hat + 3 N k hat , vector v = 9 m/s i hat

2. Relevant equations

P = F * V

3. The attempt at a solution

P =(4*9) +3

Also tried

P = SQRT(4^2+3^2) * 9
I guess the problem is I don't know how to convert the vector 4i+3j into a force.

2. Oct 14, 2008

### G01

That vector is the force. You have a force with an x component of 4N and a y component of 3N.

In order to find the power you need to find the dot product of F and v:

$$P=\vec{F}\cdot\vec{v}=F_xv_x+F_yv_y$$

It seems like this was what you were trying to do in your first attempt. You made one small mistake. HINT: What is $v_y$?