# Work and a cylinder

#### ViewtifulBeau

A homogeneous cylinder of radius 30cm and mass 40kg is rolling without slipping along a horizontal floor at 2.4m/s. How much work is needed to stop the cylinder?

work = delta_KE in this case so oi figured .5 *40 * 2.4^2 = 115 J but this is not right, what should i do with the cylinder?

#### ViewtifulBeau

i still can not figure this one out.

#### lightgrav

Homework Helper
Besides KE of the center-of-mass moving in translation (linear),
you also have KE of the extended mass moving AROUND the c.o.m.

KE_rotation = 1/2 I (omega)^2

#### ViewtifulBeau

i did this and found omega to be 8 rad/s and I to be 1.8 then i found the KE to be 57.6 this is now right either.

#### lightgrav

Homework Helper
"Besides" the old linear KE there's now rotational KE, ALSO.
The total KE is the SUM : KE_linear + KE_rotation

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