Finding angular speed from torque and angular displacement

[riseofphoenix]

What is given:

Torque: τ = 34.5 N * m
Inertia: I = 0.130 kg * m²
Angular speed: ω = ?
Work done by a constant Torque: τΔθ = (1/2)Iω_f² [STRIKE]- (1/2)Iω_i²[/STRIKE]
Angular displacement: Δθ = 17.1 rev/s = 107.442 rad/sτΔθ = (1/2)Iω_f²
(34.5)(107.442) = (0.5)(0.130)ω_f²
3706.765 = 0.065ω_f²
57027.156 = ω_f²
238.8 = ω

It's still wrong :(

 

[SHISHKABOB]

Δθ is 17.1 revolutions. You need to convert that to radians.

 

[Doc Al]

Make sure your angular displacement is in radians, not revolutions.

 

[grzz]

Change 17.1rev's to ... radians's.

 

[Doc Al]

3x should be enough

 

[riseofphoenix]

3x should be enough

Wait what? :(

 

[riseofphoenix]

Change 17.1rev's to ... radians's.

I just did and it's still wrong

 

[Doc Al]

I just did and it's still wrong

Show what you did.

 

[grzz]

If you show your work help may be given.

 

[riseofphoenix]

Show what you did.

B]What is given:[/B]

Torque: τ = 34.5 N * m
Inertia: I = 0.130 kg * m²
Angular speed: ω = ?
Work done by a constant Torque: τΔθ = (1/2)Iω_f² [STRIKE]- (1/2)Iω_i²[/STRIKE]
Angular displacement: Δθ = 17.1 rev/s
Conversion (17.1 x 2 x π) rad/s = 107.442

τΔθ = (1/2)Iω_f²
(34.5)(107.442) = (0.5)(0.130)ω_f²
3706.765 = 0.065ω_f²
57027.156 = ω_f²
238.8 = ω

 

[riseofphoenix]

If you show your work help may be given.

But I just did

 

[Doc Al]

Looks like they want the speed in rev/s, not rads/sec.

 

[riseofphoenix]

Looks like they want the speed in rev/s, not rads/sec.

Sooo...I don't convert angular displacement?

 

[Doc Al]

Sooo...I don't convert angular displacement?

Convert your answer for ω from rad/s to rev/s.

 

[riseofphoenix]

Convert your answer for ω from rad/s to rev/s.

τΔθ = (1/2)Iω_f²
(34.5)(107.442) = (0.5)(0.130)ω_f²
3706.765 = 0.065ω_f²
57027.156 = ω_f²
238.8 rad/s = ω

238.8/2π rev/s = ω
38 rev/s = ω

Awesome
Thanks!