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March 2, 2015

March 2, 2015

Posted by **Emily** on Friday, July 30, 2010 at 3:36pm.

1. A particle is acted on by two torques about the origin: τ1 has a magnitude of 4.5 N·m and is directed in the positive direction of the x axis, and τ2 has a magnitude of 1.4 N·m and is directed in the negative direction of the y axis. What are the magnitude and direction of d/dt, where is the angular momentum of the particle about the origin?

2. A sanding disk with rotational inertia 1.3 10-3 kg·m2 is attached to an electric drill whose motor delivers a torque of 9 N·m about the central axis of the disk. What are the following values about the central axis at the instant the torque has been applied for 140 ms?

(a) the angular momentum of the disk

in kg·m2/s

(b) the angular speed of the disk

in rad/s

- Physics -
**bobpursley**, Friday, July 30, 2010 at 5:37pmYou failed to mention moment of inertia. I recommend you reread that section, it is what imposes resistance to change of angular motion.

Torque=momentinertia*alpha (alpha is angular acceleartion, in radians/sec^2)

Torque*time=momentinertia*change angular velocity

angular speed final=initialangular speed +alpha*time

angular displacement=intial angular speed*time+1/2 alpha *Time^2

MEMORIZE these, understand them. Make flash cards, these are the equations of motion.

2.a)angular momentum =momentinertia (intial w+alpha*time)

but alpha=torque/moment of inertia (the first equation you should memorize, above).

solve.

b wfinal=alpha*time

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