# Net Force of an Object using position function and momentum principle

1. Feb 1, 2010

### leejqs

1. The problem statement, all variables and given/known data
A 2.80 kilogram mass is moving in a plane, with its x and y coordinates given by x = 4.50t2 - 1.15 and y = 2.90t3 + 1.95, where x and y are in meters and t is in seconds. Calculate the magnitude of the net force acting on this mass at t = 2.05 seconds

2. Relevant equations

Change in momentum (p) = Fnet * Change in time

3. The attempt at a solution
In taking the derivatives of the y position and x position separately, I now have the velocity functions. When plugging in t=2.05 to these velocity functions, I found the y and x component velocities. By using the Pythagorean theorem, I found the magnitude of the velocity, then multiplied that magnitude by the mass, 2.8kg, to find the magnitude of the momentum of the object.

I have this momentum (114.7 N) equal to the net force times the time. However, when I divide 114N/2.05seconds, my answer of 55.9 N is not correct.

Any suggestions or hints would be greatly appreciated!! Thanks!