Calculate the frictional torque of the record player

[Noor123]

URGENT! rotational kinematics

A record player is spinning at 33 rpm when the motor is switched off. After 5.9 seconds the angular speed has decreased to 20 rpm. Calculate the frictional torque if the record player can be treated as a solid wheel of mass 5.5 kg and radius 14 cm.


A. 1187.62712 Nm
B.0.01244 Nm
C. 0.04752 Nm
D. 2375.25424 Nm
E. 0.11876 Nm


Which one?

 

[hage567]

Show us your work. We don't give out answers here. We will help you figure it out.

 

[Noor123]

omege final = 3.45 rad/sec

omega initial = 2.094 rad/sec

omega final = omega initial + alpha x delta t

2.094 = 3.45 + 5.9 alpha

alpha = -0.230


torque = I x alpha

mR^2 x alpha
(0.1078) (-0.229)
= -0.02468

?? none of these answers

 

[Noor123]

Plzz Hurrrrryyyy Folks!

 

[hage567]

You are not using the right moment of inertia. For a solid wheel it should be 0.5MR^2.

 

[Astronuc]

Refer to http://hyperphysics.phy-astr.gsu.edu/hbase/icyl.html#icyl

and http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html#cmi and generally

http://hyperphysics.phy-astr.gsu.edu/hbase/mi.html

I(cyl) = 1/2 mr²

Make sure units are consistent.

 

[Noor123]

Ok what about this?

PLZ QUICK

A solid sphere of mass 4.0 kg and radius 0.12 m starts from rest at the top of a ramp inclined 15 degrees, and rolls without slipping to the bottom. The upper end of the ramp is 2.7 m higher than the lower end. What is the linear speed of the sphere when it reaches the bottom of the ramp?

A. 132.3 m/s
B. 6.15 m/s
C. 7.27 m/s
D. 7.67 m/s
E. 37.8 m/s


i 've tried PE = 1/2 mv2 + 1/2 Iw2

but nothing worked please HELP!

 

[hage567]

What did you use for I? Did you put w in terms of v?