Hi everyone,(adsbygoogle = window.adsbygoogle || []).push({});

I am stuck on two fairly easy questions that I hope someone will be able to help me with.

Questions:

1) How much angular impulse must be supplied by the hamstrings to bring a leg swinging at 8 rad/s to a stop, given that the leg's moment of inertia is 0.7 kg-m^2 ?

my solution:

angular impulse = change in angular momentum

Tt = Iw2 - Iw1 (the numbers 2 & 1 are supposed to be subscripts standing for final and initial; I=moment of inertia; w=angular velocity)

Tt = 0 - (.7)(8)

= -5.6 kg-m^2/s

what did I do wrong?

2) A 7.27kg shot makes seven complete revolutions during its 2.5 second flight. If its radius of gyration is 2.54 cm, what is its angular momentum?

my solution:

H = mk^2w (m=mass; k=radius of gyration; w=angular velocity; H = angular momentum)

7 revolutions = (360degrees x 7)/57.3

= 43.979 rad

H = (7.27)(.0254^2)(43.979/2.5sec)

= .0825 kg-m^2/s

what did I do wrong?

thanks.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Angular impulse and angular momentum questions

**Physics Forums | Science Articles, Homework Help, Discussion**