A 200 g, 20 cm diameter plastic disk is spun on an axle through its center by an electric motor. What torque must the motor supply to take the disk from 0 rpm to 1800 rpm in 4.0s?

Respuesta :

Answer: The torque required is 0.0471 N m.

Explanation:

Mass of the disc = 200 g = 0.2 kg (1 kg =1000 g)

Radius of the disc =[tex]\frac{Diameter}{2}[/tex]= 10 cm = 0.1 m(1 m = 100 cm)

Angular acceleration = [tex]\alpha [/tex]

[tex]\alpha =\frac{2\pi\times 1800}{60 \times 4 sec}=15\pi rad/s^2[/tex]

Moment of inertia = [tex]\frac{1}{2}\times mass\times (radius)^2=\frac{1}{2}\times0.2 kg\times (0.1 m)^2=0.001 kg m^2[/tex]

[tex]Torque=\alpha \times I=0.001 kg m^2\times 15\times 3.14 rad/s^2r=0.0471 N m[/tex]

The torque required is 0.0471 N m.

The value of the torque in the question is given as 0.0471N/m

The mass = 200 grams

Convert to kg = 0.2 kg

Radius = diameter/2

= 20/2 = 10cm

convert to meters = 0.1m

Angular acceleration

1800/4 = 450

450/60sec

= 7.5rot/sec²

7.5*2π

= 47.14

The moment of Inertia

I = 1/2mr²

= 1/2*0.2*0.1²

= 0.0001kg

The value of the torque

= 0.001 * 47.14

= 0.04714N.M

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