# Homework Help: Force problem

1. Sep 30, 2007

### tarzanna

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

A 2.75 kg object is moving in a plane, with its x and y coordinates given by x = 7t^2 - 4 and y = 5t^3 + 1, where x and y are in meters and t is in seconds. Find the magnitude of the net force acting on this object at t = 2.35 s.

2. Relevant equations

F=ma

3. The attempt at a solution

I took the 2nd derivative of each posn eqn and then substituted 2.35s for t to get accel; multiplied each accel by 2.75 kg to get Fx and Fy; then took the sqrt of (Fx^2 + Fy^2) to get magnitude.

I am not sure how to proceed. Thanks for any help!

2. Sep 30, 2007

### Staff: Mentor

Write the answer down and turn the question in, you already got it.

3. Sep 30, 2007

### tarzanna

Thanks. I calculated the answer to be 104.5 N but it was marked as incorrect by the web program I use to turn in assignments. So something isn't right.

4. Sep 30, 2007

### Staff: Mentor

I got 198 N, you must've made an arithmetic error.