Homework Help: Calculate the frictional torque of the record player

1. Nov 18, 2007

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?

2. Nov 18, 2007

hage567

3. Nov 18, 2007

Noor123

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

4. Nov 18, 2007

Noor123

Plzz Hurrrrryyyy Folks!!

5. Nov 18, 2007

hage567

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

6. Nov 18, 2007

Astronuc

Staff Emeritus
7. Nov 18, 2007

Noor123

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