# Homework Help: Force pulling a pendulum

1. Oct 31, 2013

### nx01

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

A 2.0 kg pendulum ball is pulled 30° from the vertical by a horizontal force Fpull. What is the magnitude of Fpull?

2. Relevant equations

F=ma

3. The attempt at a solution

I'm rather lost with this one - I'm not even sure how to classify it. Any help at all - even a point in the right direction - would be greatly appreciated.

2. Oct 31, 2013

### physics&math

Unless the problem says otherwise, assume Fpull is at a 90° angle from the vertical.

Force diagram. You'll have three forces: tension, Fpull, and the force of gravity. The tension will have two components.

3. Oct 31, 2013

### physics&math

sorry, misread the post. it said horizontal. So it is definitely a right angle from the vertical

4. Oct 31, 2013

Yes -- diagram it.

5. Nov 1, 2013

### nx01

Hi all, thanks for your input. Is it right to assume that the force of gravity = the y component of the tensional force, and that the force applied to the ball = the x component of the tensional force? If so, how can I calculate Tx without knowing the magnitude of T? (If my assumptions are correct, I can calculate Ty using Fg, but I don't know how that value could help me.)

6. Nov 1, 2013

### haruspex

Yes.
If T is the total tension and the angle is 30o, what in terms of T are Tx and Ty?

7. Nov 1, 2013

### nx01

If the ball is 30o from the vertical to the right, then T is oriented 130o from the positive direction of the x-axis. Then Tx =Tcos130, and Ty=Tsin130?

8. Nov 1, 2013

### haruspex

No, not 130. How did you calculate that?

9. Nov 1, 2013

### nx01

Oops, I meant 120. I've attached a picture (.jpg) showing how I calculated the angle.

Thanks for your responses so far!

#### Attached Files:

• ###### Note_20131101_221130_01.jpg
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10. Nov 1, 2013

### haruspex

Yes, that's better.

11. Nov 1, 2013