# Magnitude of the net force

1. Oct 6, 2009

### Chuck 86

A 3.40 kilogram mass is moving in a plane, with its x and y coordinates given by x = 4.85t2 - 1.05 and y = 3.25t3 + 2.10, 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 = 2.10 seconds.

I dont know if im supposed to plug in 2.10 for t at the begining because i got a relativly different answer when i tried that

2. Oct 6, 2009

### rl.bhat

To find the force on the mass, first of all you have to find the acceleration of the mass.
Find ax = d^2x/dt^2 and ay = d^2y/dt^2 at given time t. Find net acceleration and then the net force.

3. Oct 6, 2009

### Chuck 86

So i find the derrivative of the x and y then plug in t=2.10?

4. Oct 6, 2009

### rl.bhat

Yes. Find the derivative twice to get the acceleration.

5. Oct 6, 2009

i see thanks

6. Oct 8, 2009

### Chuck 86

After that i take the sum of the accelerations at 2.10 multiplied by the mass 3.40?

7. Oct 8, 2009

### rl.bhat

To find the net acceleration you have to find the vector sum of ax and ay.

8. Oct 8, 2009

### Chuck 86

i found that to be 9.7+ 40.95=50.65. do i take 50.65 multiplied by 3.40kg's to get the answer of the net force in newtons?

9. Oct 8, 2009

### rl.bhat

ax and ay are perpendicular to each other. You can't add then directly to get the resultant acceleration.