# Center of mass

1. Sep 15, 2007

### Edwardo_Elric

1. The problem statement, all variables and given/known data
A model airplane has a momentum given by
$$[(0.25 kg . m/s^3)t^2 - (0.75 kg . m/s^2)t]\hat{i}$$
a.) What are the x- , y- , and z- components of the net force on the airplane?
b.) At what time t is the x-component of the net force on the airplane equal to zero?

2. Relevant equations
$$\sum F = \frac{d\vec{p}} {dt}$$

3. The attempt at a solution
a.) i used the derivative to get :
Fx = 2(0.25m/s^3)t - (0.75m/s^2) so the x- component of net force
Fy = 0
Fz = 0
since they are the j hat and k hat where it is not given

b.) when Fx = 0;
0 = 2(0.25m/s^3)t - (0.75m/s^2)
2(0.25m/s^3)t = (0.75m/s^2)
t = 1.5s

2. Sep 15, 2007

### HallsofIvy

Staff Emeritus
Looks good to me!