# Centripetal Force Question

• Kaos_Griever
In summary, the problem involves a 1.0kg ball attached to a vertical rod by two strings forming an equilateral triangle. The tension in the upper string is known, but the tension in the lower string is unknown. The net force on the ball can be calculated using the equation F = mv^2 / r, where m is the mass, v is the velocity, and r is the radius. It is important to draw a free-body diagram to identify all the forces acting on the ball, including the force of gravity. However, it is unclear if the system is rotating at a specific speed or just fast enough for the lower string to be taut.

#### Kaos_Griever

Homework Statement
A 1.0kg ball is attached to a rigid vertical rod by the means of two massless strongs each 1.0m long. The strings are attached to the rod at points 1.0m apart. The system is rotating about the axis of the rod, both strings being taut and forming an equilateral triangle with the rod. The tension in the supper string is What is the tension in the lower string? What is the net force on the ball? What is the speed of the ball?

Relevant equations
The only equation I can think of is F = mv^2 / r
where m = mass, r = radius, v = velocity, F = Centripetal Force

The attempt at a solution
I'm not sure how to do the entire question... does finding the tension need an angle? Because the string is not at the horizontal...

At first glance, (and maybe I'm missing something) but it seems that something is missing. If you spin the rod faster and faster (once you've reached the point at which both strings are taut), the tension in the strings will increase until they finally break, and will continue to form an equilateral triangle.

Is it implied in the problem that the system is rotating "just fast enough" for the lower string to be taut?

However, on problems where forces are important, it's a good idea to draw a free-body diagram. What forces are acting on the ball? (You're missing one; usually one which is obvious)

No other forces have been given to me in the question. I am also not sure of the forces that will be acting on the free body diagram of the ball? Would it only be the force of gravity, the normal force, and the forces of the strings...?

Yes, the force of gravity = you just had a mass there; I was making sure you were including that force.

Kaos_Griever said:
No other forces have been given to me in the question. I am also not sure of the forces that will be acting on the free body diagram of the ball? Would it only be the force of gravity, the normal force, and the forces of the strings...?
I believe you left out a given..the tension in the upper string is ?