# A model train, with a mass of 4 kg, is moving on a circular track with a radius of 3 m. If the train's kinetic energy changes from 15 j to 6 j, by how much will the centripetal force applied by the tracks change by?

Sep 11, 2016

the centripetal force change from 10n to 4n, or decrease at 2,5 times.

#### Explanation:

Kinetic energy is $\frac{m {v}^{2}}{2}$

The first velocity ${v}_{1} = \sqrt{15 \cdot \frac{2}{4}} = \sqrt{7 , 5}$

${v}_{2} = \sqrt{6 \cdot \frac{2}{4}} = \sqrt{3}$

The centripetal force is $F = m {v}^{2} / r$

${F}_{1} = 4 \cdot 7 , \frac{5}{3} = 10 n$
${F}_{2} = 4 \cdot \frac{3}{3} = 4 n$