angular momentum kind of stuff

[Sarahisme]

just a quick phys question

 

A wheel mounted on an axis that is not frictionless is initially at rest. A constant external torque of 50 N . m is

applied to the wheel for 20 s, giving the wheel an angular velocity of 600 rev/min. The external torque is then re-moved, and the wheel comes to rest 120 s later.

Find (a) the moment of inertia of the wheel, and (b) the frictional

torque, which is assumed to be constant.

 

 

and i get (sorry don't have time to write out complete working)

 

a) 60/pi kg.m^2

b) 10 N.m

 

is wrong or right? lol

 

Sarah

[Sarahisme]

acutally i am not so sure maybe it is

a) 300/7pi kg.m^2

b) 50/7 N.m

[Sarahisme]

lol this is fairly urgent, :S as in within the next 8 hours noooo :S

[swansont]

Looks like your second set of answers are OK.

 

The net torque is the applied + frictional, and you can solve for the two accelerations (pi rad/ s² for the first part, and pi/6 rad/ s²) for the second.

[Sarahisme]

right o thanks swansont

 

i just get a little worried about my answers when i am doing them late at night