Finding an expression for torque

1. Apr 21, 2012

Lucy Yeats

1. The problem statement, all variables and given/known data

http://www.physics.ox.ac.uk/users/yassin/mechanics/problems/probs6_2011.pdf [Broken]

Q 2b.

2. Relevant equations

3. The attempt at a solution

T is torque and J is angular momentum.
T=dJ/dt=I dω/dt

I tried solving dω/dt=ωk to get dω/dt=ce^kt, but this may not help.

Last edited by a moderator: May 5, 2017
2. Apr 21, 2012

Curious3141

They represented torque as N.

You're given N = kω ---equation 1

You also know that N = -I$\frac{dω}{dt}$ ---equation 2
(the negative sign is to keep N positive since they're concerned with the numerical value for torque).

You can equate equations 1 and 2 to get kω = -I$\frac{dω}{dt}$

and solve the differential equation. Remember to apply the given bounds using definite integrals on both sides after separating the variables ω and t.

After that, express k in terms of the other variables, and put this back into equation 1 to get N.

Last edited by a moderator: May 5, 2017
3. Apr 22, 2012

Lucy Yeats

Great, I've got the right answer now.

Thank you very much! :-)

4. Apr 22, 2012

Curious3141

You're welcome.