- #1
max1205
- 14
- 0
Hi everyone,
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.
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.