# Homework Help: Max tension in rope for a spinning object, whats the max kinetic energy possible?

1. Mar 10, 2012

### tprofl

1. The problem statement, all variables and given/known data
An object is constrained by a cord to move in a circular path of radius 0.5m on a horizontal frictionless surface. The cord will break if tension exceeds 16N. The maximum kinetic energy the object can have is:

2. Relevant equations
KE=1/2mv^2
U=mgh

3. The attempt at a solution
Because the object is spinning in a horizontal circle, you may take the tension at any point. Potential can equal kinetic, mgh=1/2mv^2, but I cant figure out how to start this problem.

2. Mar 10, 2012

### cepheid

Staff Emeritus
Welcome to PF!

I can't figure out what you're saying in your solution attempt, in particular, the bit about taking the tension "at any point."

Furthermore, since the circle is horizontal, the object never changes height, meaning that its gravitational potential energy is constant. Potential energy, therefore, is somewhat irrelevant to the problem.

Try, instead, to think of it this way: since kinetic energy depends on speed, the object's maximum kinetic energy is going to depend on its maximum possible speed. What determines the speed of an object in uniform circular motion? Hint: what kind of force is the tension in the rope providing in order to produce circular motion?

3. Mar 10, 2012

### PeterO

Because this object is on a horizontal table, its gravitational potential energy (mgh) doesn't ever change.

The centripetal force required to keep an object in circular motion is given by mv2/R

I was always interested in comparing the kinetic energy formula 1/2 mv2 as they both contain the mv2 expression

By comparing and combining those two expressions/formulas I think you can discover the answer you seek.