# Two skaters of equal mass grab hands and spin

1. Feb 15, 2015

### Calpalned

1. The problem statement, all variables and given/known data
On an ice rink two skaters of equal mass grab hands and spin in a mutual circle once every 2.5s. If we assume their arms are each 0.80m long and their individual masses are 55.0kg , how hard are they pulling on one another?

2. Relevant equations
$a_c = \frac {v^2}{R}$
$v = \frac {D}{T}$
$D = 2 \pi R$

3. The attempt at a solution
With R = 0.8, and m = 55kg, I plugged it into $F = m a = m \frac {v^2}{R}$ and I got the right answer. However, I don't understand why I have to use m = 55kg, rather than 110 kg (as there are two people spinning).

Last edited: Feb 15, 2015
2. Feb 15, 2015

### haruspex

Because the force acts on each. Each applies a force $m \frac {v^2}{R}$ to the other, where m is the mass of one.