Circular Platform
A horizontal circular platform (M = 112.1 kg, r = 3.11 m) rotates about a frictionless vertical axle. A 95.3 kg student walks slowly from the rim of the platform toward the center. The angular velocity of the system is 2.1 rad/s when the student is at the rim.
Find the angular velocity of the system when the student is 1.39 m from the center.
4.23 rad/s
Find the angular velocity of the system when the student is 1.39 m from the center.
4.23 rad/s
Discussion
NEW
Anonymous 1
How do you do this problem?
NEW
m= mass of student
M= mass of platform
r1= radius of platform
r2= new radius (m from center)
w1= angular velocity
w2= ??? (new angular velocity)
Solve for 1st I of the student at rim using
1/2(m*r^2) + M*r^2
[Mine was 1333.29 kg*m^2]
Find the 2nd I of student at new location
1/2(m*r^2) + M*r2^2 <- 2nd half uses r2 not r
[Mine was 570.13 kg*m^2]
Then solve for w2
w2=I1*w1/I2
[Mine was 7.72 rad/s]
Hope that helps :3
NEW
Help plz
Could anybody tell me what I'm doing wrong, I'm following
all the right steps and nothing is working.
M=73.1
m=65.3
r=3.11
r2=1.27
wi=4.1
Ii=.5(73.1(3.11)^2 + (65.3)(3.11)^2
=981
If= 5(73.1(.3.11)^2 + (65.3)(1.27)^2
=448.8
wf=4.1(981/448.8)=8.96rad/s
but it is wrong...
NEW
the equations are correct but the masses are switch: for I1 the equation is
1/2(M*r^2)+m*r^2
For I2 the equation is
1/2(M*r^2)+m*r2^2
then use
w2=I1w1/I2
to get the answer
NEW
Shoot, sorry about that! =/
NEW
Thanks Deliah and Greg! That was a big help!
Anonymous 1
How do you do this problem?
NEW
m= mass of student
M= mass of platform
r1= radius of platform
r2= new radius (m from center)
w1= angular velocity
w2= ??? (new angular velocity)
Solve for 1st I of the student at rim using
1/2(m*r^2) + M*r^2
[Mine was 1333.29 kg*m^2]
Find the 2nd I of student at new location
1/2(m*r^2) + M*r2^2 <- 2nd half uses r2 not r
[Mine was 570.13 kg*m^2]
Then solve for w2
w2=I1*w1/I2
[Mine was 7.72 rad/s]
Hope that helps :3
NEW
Help plz
Could anybody tell me what I'm doing wrong, I'm following
all the right steps and nothing is working.
M=73.1
m=65.3
r=3.11
r2=1.27
wi=4.1
Ii=.5(73.1(3.11)^2 + (65.3)(3.11)^2
=981
If= 5(73.1(.3.11)^2 + (65.3)(1.27)^2
=448.8
wf=4.1(981/448.8)=8.96rad/s
but it is wrong...
NEW
the equations are correct but the masses are switch: for I1 the equation is
1/2(M*r^2)+m*r^2
For I2 the equation is
1/2(M*r^2)+m*r2^2
then use
w2=I1w1/I2
to get the answer
NEW
Shoot, sorry about that! =/
NEW
Thanks Deliah and Greg! That was a big help!