Question

One question.... physics

Answer 1

A solid disk of mass \(\color{#339999}{\rm m_1=9.1~kg}\) and radius \(\color{#339999}{\rm R=0.25~m}\)
is rotating with a constant angular velocity of \(\color{#339999}{\rm \omega=32~rad/s}\).
A thin rectangular rod with mass \(\color{#339999}{\rm m_2=3.4~kg}\) and length
\(\color{#339999}{\rm L = 2R = 0.5~m}\) begins at rest above the disk and is dropped
on the disk where it begins to spin with the disk.


I have found that: (And all of this is exactly correct I checked)


[1] The initial angular momentum of the rod and disk system.
9.10 kg-m^2/s

[2] The initial rotational energy of the rod and disk system.
145.6 J

[3] The final angular velocity of the disk.
24.91 rad/s

[4] The final angular momentum of the rod and disk system.
9.10 kg-m^2/s

[5] The final rotational energy of the rod and disk system.
113.32 J

Answer 2

The only thing that I need help with, is question 6 (above).


The rod took t = 6.2 s to accelerate to its final angular speed with
the disk. What average torque was exerted on the rod by the disk?

Answer 3

how do we define torque?

Answer 4

Torque = I * α = (1/12)*m2*L^2 * w\(_f\) / t

am I right ?

Answer 5

im not uptodate on my physics equations, so id have to google to verify

Answer 6

if we had applied a constant torque, for 6.2 seconds, what amount of torque would have got us to where we ended up?

Answer 7

yes, \(\tau = I \; \alpha\)

they should be opposite and equal, if you calculate them for both rod and disc.

Answer 8

the torque for rod and torque for disk are equivalent, you mean ?

Answer 9

equal and opposite, ie Newton's 3rd Law in a rotational context.

Answer 10

ill defer to the more qualified :)

Answer 11

I keep loosing it, sorry

Answer 12

\(\tau = I \; \alpha\)
\(\tau = (1/12)M_2*L^2 *w_f/t\)

am I right?

Answer 13

\(\tau = (1/12)3.4*L^2 *24.91/6.2\)

and I have to calculate the L, based on:
Li = Lf = I\(_{disk}\) * w\(_0\) = (1/2)(m1)(R^2)w0

Answer 14

L = 1/2 * 9.1 * 0.25^2 * 32 = 9.1

\(\tau = (1/12)3.4*9.1^2 *24.91/6.2\)

Answer 15

is it
or


i think you take it as the latter, hence the \(\dfrac{1}{12}\)