# Uniform circular motion - 2 dimensional - 2 forces

1. Apr 12, 2012

### finitefemmet

An object moves in the xy-plane in a uniform circular motion. We know that there is two forces action upon the object. One we have that is F1, F2 is unknown. Both vectors

speed : 4m/s
mass : 1kg
F1 : 10 i N (i as in x-direction vector)
F2 : ? (bound to be in the xy-plane)

How do I calculate F2, and I have to calculate it when the angle between the rope and the x-axis is 0, Pi/2 , Pi. The rope has no mass by the way. The motion is counter-clockwise, and the angle is zero when the ball is at the positive side of the x-axis (given that origin is in the middle of the motion).

Thank you!

Excuse my poor english

2. Apr 12, 2012

### darkxponent

Can you tell us what the acceleration of particle if it is in a Uniform circular motion?

3. Apr 12, 2012

### ashishsinghal

Hey finitefemmet,

As the speed is given you can calculate the centripetal force required for the circular motion. Then find F2 such that F1 + F2 is equal to the required force and in the given direction.

Try solving after this.

4. Apr 12, 2012

### finitefemmet

Okey,

so I have calculated that the net force for the circular motion is 4N.... -4(j) if we are at angle zero position.

Now correct me if I am wrong on this:

When the angle is 0, that is when the ball is on the right side of origin on the x-axis.
The force is then pointing too origin and that is negative x-direction. F2 is then : -4(j) - 10 (i).

Minus 10 too "cancel" out the y-axis force and -4(j) too get the right net force.

And so on for the rest of the angles

Right track?

Thanks for the quick response!

5. Apr 14, 2012

### darkxponent

Is that correct?

6. Apr 15, 2012

### finitefemmet

Well

F = (m*v2) / r
F = (1*4^2) / 4 = 4
And the force is pointing towards the center.

7. Apr 15, 2012

### darkxponent

that is why it is -4(i) not (j)

8. Apr 16, 2012

### finitefemmet

My mistake, you are absolutely right!

But now that is solved, the rest of my thinking should be okey?

9. Apr 16, 2012

### darkxponent

yeah rest is right. The only mistake was this one