# PHysics PHysics Physics Physics Torque

1. Nov 3, 2004

### envscigrl

Here is my problem:
A 2.50g particle moves in a circle of radius 3.00m. The magnitude of its angular momentum relative to the center of the circle depends on time according to L = (3.5 Nm)t. Find the magnitude of the torque acting on the particle.

I know that:
T = F L
where T = torque
F is the force
L is angular momentum
I feel like this problem is more algebraic than anything. I just need something stable to start from. Pleeeeeeeeaaaase Heeeeeeelp!!

2. Nov 3, 2004

### jamesrc

I'm afraid your equation is wrong. You may be thinking of $$\vec{\tau} = \vec{r}\times\vec{F}$$, where r is the moment arm (and its a vector equation). What you need to use is the idea that the rate of change of angular momentum is equal to the torque. I hope that helps.