A propeller slows from 470 rev/min to 159 rev/min in 3.00 s. What is its angular acceleration?

Question

1. A propeller slows from 470 rev/min to 159 rev/min in 3.00 s. What is its angular acceleration?
I got 10.8504 as an answer but webassign says it is not the right answer...?

2.What is the torque on a bolt produced by a F = 15 N force exerted perpendicular to a wrench that is l = 30 cm long, as shown below?

3.A toy rotates at a constant 13 rev/min. Is its angular acceleration positive, negative, or zero?
I know it is either negative or zero.

4. An automobile wheel with a 9.00-cm radius, as shown below, rotates at 1.00 rad/s. How fast does a point 4.00 cm from the center travel?

Answer 1

1)

Initial speed of the propeller,N1=470 rev/min

Initial angular velocity of the propeller,ω1=2πN1/60

                                                                         =2πx470/60

                                                                         =49.22 rad/s

Final speed of the propeller,N2=159 rev/min

Final angular velocity of the propeller,ω2=2πN2/60

                                                                         =2πx159/60

                                                                         =16.65 rad/s

Time,t=3s

Angular acceleration,α=(ω2-ω1)/t

                                         =(16.65-49.22)/3

                                         =-10.8565 rad/s^2

Answer 2

2)

Force ,F=15 N

 

Perpendicular distance,d=30 cm = 0.3 m

Torque,T=Fxd

               =15x0.3

               =4.5 N-m

Answer 3

6^3) Rotational speed is constant Angular acceleration is zero 4) Velocity,v=(r-x)ω =(9-4)*10^-2*1 =0.05 m/s