Physics Problem Involving Moment and Acceleration

[taylorkrauss]

A uniform board length L hinged about its lower end, held at θ above the horizontal is released from rest. As it passes through the horizontal what is the tangential acceleration of its outer tip?



At first when I attempted this, I applied conservation of energy.
(1/2)mv^2+mgh=(1/2)mv^2 + mgh
but I did not get an answer.
Then I decided could the answer just be L*gravity?? Any help given will be much apreciated! Thank you!

 

[tiny-tim]

welcome to pf!

hi taylorkrauss! welcome to pf!

your kinetic energy must include the rotational KE:

KE = 1/2 mv_c.o.m² + 1/2 I_c.o.mω² = 1/2 I_c.o.rω² ​

 

[gneill]

You're looking for tangential acceleration, not velocity. So think about the moment of inertia, where the center of rotation is, and what forces are acting to produce a torque at the instant in question.