A 0.0215 m diameter coin rolls up a 20.0 degree inclined plane. The coin starts with an initial angular speed of 55.2 rad/ s and rolls in a straight line without slipping. How much vertical height does it gain before it stops rolling?

Respuesta :

Answer:

The coin will reach a vertical height of 0.027 meters before it stops rolling.

Explanation:

Let suppose that coin-ground system is a conservative system and begins at a height of zero. Since the coin is experimenting a general plane motion, which is a combination of translation and rotation. By Principle of Energy Conservation we have the following model:

[tex]K_{T}+K_{R} = U_{g}[/tex] (1)

Where:

[tex]K_{T}[/tex] - Translational kinetic energy at the bottom of the incline, in joules.

[tex]K_{R}[/tex] - Rotational kinetic energy at the bottom of the incline, in joules.

[tex]U_{g}[/tex] - Gravitational potential energy at the top of the incline, in joules.

By definitions of Kinetic and Gravitational Potential Energy we expand (1):

[tex]\frac{1}{2}\cdot I \cdot \omega ^{2} + \frac{1}{2}\cdot m\cdot R^{2}\cdot \omega^{2} = m\cdot g\cdot h[/tex] (2)

Where:

[tex]I[/tex] - Momentum of inertia of the coin, in kilogram-square meters.

[tex]\omega[/tex] - Angular speed, in radians per second.

[tex]R[/tex] - Radius of the coin, in meters.

[tex]m[/tex] - Mass, in kilograms.

[tex]g[/tex] - Gravitational acceleration, in meters per square second.

[tex]h[/tex] - Height reached by the coin, in meters.

The momentum of inertia of the coin is calculated by:

[tex]I = \frac{1}{2}\cdot m\cdot r^{2}[/tex] (3)

Then, we expand and simplify (2):

[tex]\frac{3}{4}\cdot R^{2}\cdot \omega^{2} = g\cdot h[/tex]

[tex]h = \frac{3\cdot R^{2}\cdot \omega^{2}}{4\cdot g}[/tex]

If we know that [tex]R = 0.0108\,m[/tex], [tex]\omega = 55.2\,\frac{rad}{s}[/tex] and [tex]g = 9.807\,\frac{m}{s^{2}}[/tex], then the height reached by the coin is:

[tex]h = 0.027\,m[/tex]

The coin will reach a vertical height of 0.027 meters before it stops rolling.