# A model train, with a mass of 3 kg, is moving on a circular track with a radius of 5 m. If the train's kinetic energy changes from 32 j to 12 j, by how much will the centripetal force applied by the tracks change by?

##### 1 Answer
Feb 2, 2016

${F}_{C} = 2 \frac{K E}{r} = 2 \frac{20}{5} = 8 N$

#### Explanation:

Start by writing the equation for Kinetic Energy, KE:
$K E = \frac{1}{2} m {v}^{2}$ divide by 2 on both sides
$2 K E = m {v}^{2}$ divide by r the radius of the circular track
$2 \frac{K E}{r} = m {v}^{2} / r$ now on the right what we have is the Centripetal Force ${F}_{C} = m \left({v}^{2} / r\right)$, so:
${F}_{C} = 2 \frac{K E}{r} = 2 \frac{20}{5} = 8 N$