A 392 N wheel comes off a moving truck and rolls without slipping along a highway. At the bottom of a hill it is rotating at 24 rad/s. The radius of the wheel is 0.600 m, and its moment of inertia about its rotation axis is 0.800MR2. Friction does work on the wheel as it rolls up the hill to a stop, a height h above the bottom of the hill; this work has absolute value 2600 J. Calcuate h

Respuesta :

Answer:

h=12.41m

Explanation:

N=392

r=0.6m

w=24 rad/s

[tex]I=0.8*m*r^{2}[/tex]

So the weight of the wheel is the force N divide on the gravity and also can find momentum of inertia to determine the kinetic energy at motion

[tex]N=m*g\\m=\frac{N}{g}\\m=\frac{392N}{9.8\frac{m}{s^{2}}}[/tex]

[tex]m=40kg[/tex]

moment of inertia

[tex]M_{I}=0.8*40.0kg*(0.6m} )^{2}\\M_{I}=11.5 kg*m^{2}[/tex]

Kinetic energy of the rotation motion

[tex]K_{r}=\frac{1}{2}*I*W^{2}\\K_{r}=\frac{1}{2}*11.52kg*m^{2}*(24\frac{rad}{s})^{2}\\K_{r}=3317.76J[/tex]

Kinetic energy translational

[tex]K_{t}=\frac{1}{2}*m*v^{2}\\v=w*r\\v=24rad/s*0.6m=14.4 \frac{m}{s}\\K_{t}=\frac{1}{2}*40kg*(14.4\frac{m}{s})^{2}\\K_{t}=4147.2J[/tex]

Total kinetic energy  

[tex]K=3317.79J+4147.2J\\K=7464.99J[/tex]

Now the work done by the friction is acting at the motion so the kinetic energy and the work of motion give the potential work so there we can find height

[tex]K-W=E_{p}\\7464.99-2600J=m*g*h\\4864.99J=m*g*h\\h=\frac{4864.99J}{m*g}\\h=\frac{4864.99J}{392N}\\h=12.41m[/tex]

The height above the bottom of the hill rolled up by the wheel is 15.1 m.

The given parameters;

  • weight of the wheel, W = 392 N
  • speed of the wheel at the bottom, v = 24 rad/s
  • radius of the wheel, R = 0.6 m
  • moment of inertia of the wheel, I = 0.8 MR²

The mass of wheel, M, is calculated as follows;

[tex]W = Mg\\\\M = \frac{W}{g} = \frac{392}{9.8} = 40 \ kg[/tex]

The work-done by friction on the wheel is change in the mechanical energy of the wheel;

[tex]mgh - K.E_r = W_f\\\\mgh = W_f + K.E_r\\\\mgh = W_f + \frac{1}{2} I\omega^2 \\\\mgh = W_f + \frac{1}{2} (0.8MR^2 \omega ^2)\\\\h = \frac{W_f \ + \ 0.4MR^2 \omega ^2}{mg} \\\\h = \frac{2600 \ \ + \ \ 0.4 \times (40 )\times 0.6^2 \times (24)^2}{392} \\\\h = 15.1 \ m[/tex]

Thus, the height above the bottom of the hill rolled up by the wheel is 15.1 m.

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