An electric motor rotating a workshop grinding wheel at a rate of 176 rev/min is switched off. Assume constant angular deceleration of magnitude 2.71 rad/s^2. Through how many revolutions does the wheel turn before it finally comes to rest?

Respuesta :

Answer:

The number of revolution that the wheel turn before it stops is [tex]\bf{62.7~rad}[/tex].

Explanation:

Given:

Initial angular velocity of the motor, [tex]\omega_{i} = 176~rev/min[/tex]

Final angular velocity of the motor, [tex]\omega_{f} = 0[/tex]

Value of constant angular deceleration, [tex]\alpha = 2.71~rad/s^{2}[/tex]

Consider that [tex]t[/tex] is the time taken by the motor to come to at rest.

The equation of motion of the motor is given by

[tex]\omega_{f} = \omega_{i} - \alpha t~~~~~~~~~~~~~~~~~~~~~~~~~~~~~(1)[/tex]

Substituting the values in equation (1),

[tex]t &=& \dfrac{\omega_{i}}{\alpha}\\ &=& \dfrac{176~(\dfrac{rev}{min})(\dfrac{2 \pi~rad}{1~rev})(\dfrac{1~min}{60~s})}{2.71~rad/s^{2}}\\ &=& 6.8~s[/tex]

Consider the angle of revolution is [tex]\theta[/tex].

The equation for revolution is given by

[tex]\theta = \omega_{i}t - \dfrac{1}{2}\alpha t^{2}~~~~~~~~~~~~~~~~~~~~~~~~~(2)[/tex]

Substituting the values in equation (2),

[tex]\theta = (176~(\dfrac{rev}{min})(\dfrac{2 \pi~rad}{1~rev})(\dfrac{1~min}{60~s}))(6.8~s) - \dfrac{1}{2}(2.71~rad/s^{2})(6.8~s)^{2}\\~~&=& 62.7~rad[/tex]

The revolutions the wheel turn before it finally comes to rest will be "62.7 rad".

Velocity and Acceleration

According to the question,

Initial angular velocity, [tex]\omega_i[/tex] = 176 rev/min

Final angular velocity, [tex]\omega_f[/tex] = 0

Constant angular deceleration, α = 2.71 rad/s²

By using the equation of motion,

→ [tex]\omega_f[/tex] = [tex]\omega_i[/tex] - αt

or,

t = [tex]\frac{\omega_i}{\alpha}[/tex]

By substituting the values,

 = [tex]\frac{176\times \frac{2 \pi \ rad}{1 \ rev}\times \frac{1 \ min}{60 \ s} }{2.71}[/tex]

 = 6.8 s

hence,

By using equation of revolution,

→ θ = [tex]\omega_i[/tex] t - [tex]\frac{1}{2}[/tex] αt²

By substituting the values,

     = 176 × [tex]\frac{2 \ pi \ rad}{1 \ rev}[/tex]  × [tex]\frac{1 \ min}{60 \ s}[/tex] - [tex]\frac{1}{2}[/tex] × 2.71 × (6.8)²

     = 62.7 rad

Thus the response above is correct.  

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