# Centripital Motion

1. A 100g bead is free to slide along a 80cm piece of string ABC. Points A and B of the string are attached to a vertical pole 40 cm apart. When the pole is rotated AB becomes horizontal.

I have attached a diagram of the question.

Find the tension in the string?
Find the speed of the ball at point B?

Relevant Equations
F = mv^2/r
a = v^2/r
F = ma

Attempt:
I know that the centripital force acting on the object must be equal to the Tension acting in the horizontal direction. Also the radius of the string when the bead is at point B is a function of the angle. I also believe that the vertical force acting on the string must be equal to the downward force of gravity. Therefore so far I have:

1. radius = 40/tan0
2. a = v^2/(40/tan0) (this is when subbing in for r the above equation)
3. Ty = mg = 0.98

I am not sure where to go from here, or even if I am starting off right. Any help would be appreciated.

Thanks

## The Attempt at a Solution

#### Attachments

• 128.4 KB Views: 355

## Answers and Replies

Related Introductory Physics Homework Help News on Phys.org
1. A 100g bead is free to slide along a 80cm piece of string ABC. Points A and B of the string are attached to a vertical pole 40 cm apart. When the pole is rotated AB becomes horizontal.

I have attached a diagram of the question. Does anybody know how to put the picture of the question directly on this post?

Find the tension in the string?
Find the speed of the ball at point B?

Relevant Equations
F = mv^2/r
a = v^2/r
F = ma

Attempt:
I know that the centripital force acting on the object must be equal to the Tension acting in the horizontal direction. Also the radius of the string when the bead is at point B is a function of the angle. I also believe that the vertical force acting on the string must be equal to the downward force of gravity. Therefore so far I have:

1. radius = 40/tan0
2. a = v^2/(40/tan0) (this is when subbing in for r the above equation)
3. Ty = mg = 0.98

I am not sure where to go from here, or even if I am starting off right. Any help would be appreciated.

Thanks

Doc Al
Mentor
You have the info needed to find the sides and angles of the right triangle.

Apply Newton's 2nd law to the horizontal components.