# Dynamics of ridged bodies homework help

1. Nov 28, 2011

### biga415

hey guys, got a few different questions for you, if you can answer any of them it would be greatly appreciated!

1. a barrel of mass 2.9x10^2 kg and radius of .5m rolls down a 43 degree ramp without slipping. what is the value of the friction force acting at the point of contact between the barrel and the ramp? treat the barrel as a cylinder of uniform density.

2. the wheel of an automobile has a mass of 25 kg and a diameter of 71cm. assume that the wheel can be regarded as a uniform disk.

a) what is the angular momentum of the wheel when the automobile is traveling at 25 m/s (90km/h) on a straight road?

b) what is the torque on the wheel when the automobile is traveling at the same speed along a curve of radius 83m?

3.neutron stars spin very quickly about their axes. their high rate of spin is the result of conservation of angular momentum during the formation of the neutron star by the gradual contraction of an initially normal star.

a) suppose that the initial star is similar to the sun, with radius 8x10^8m and a rate of rotation of 2 rev/month. if this star contracts to a radius of 2x10^4m, by what factor does the moment of inertia increase? assume that the relative distribution of mass in the initial and final stars are roughly the same.

b) by what factor does the angular velocity increase?

c) what is the final angular velocity?

4.suppose that the flywheel of a gyroscope is a uniform disk of mass 250g and radius 2.5cm. the distance of the center of the flywheel from the point of support is 4cm. what is the precession frequency if the flywheel is spinning at 130 rev/s?

thanks guys!

2. Nov 28, 2011

### BruceW

The point of this forum is to give homework help, not to ask people to do it for you! You should first try the questions yourself, and show your working (preferably as clearly as possible), and then someone can tell you if/where you might have gone wrong.

3. Nov 28, 2011