| Torque, Rigid Bodies, Rotational Motion, etc.
I am completely lost on 4 of my homework problems. I just need to know how to set them up. We went through this chapter so fast that it's hard for me to remember exactly what to do.
1. A uniform 13-kg trap door is oriented horizontally and hinged as shown. (It has a length of 0.75 m) What is the magnitude of the torque on the door at the instant that the release is activated and the door can freely rotate?
2. Three forces are applied to a wheel of radius 0.350 m. One force is perpendicular to the rim, one is tangent to it, and the other one makes a 40 degree angle with the radius. What is the net torque on the wheel due to these three forces for an axis perpendicular to the wheel and passing through it's center? (The force perpendicular to the rim = 11.9 N; The force making a 40 degree angle = 14.6N; The force that is tanget to it = 8.50 N)
3. A playground mery-go-round has radius 2.40 m and moment of inertia 2100 kg. m2 about a vertical axis through it's center, and it turns with negligible friction. A child applies an 18.0 N force tangetially to the edge of the merry-go-round for 15 s. If the merry-go-round is initially at rest:
a. what is its angular speed after this 15 s interval
b. how much work did the child do on the merry-go-round
c. What is the average power supplied by the child.
4. The outstretched hands and arms of a figure skater preparing for a spin can be considered as a slender rod pivoting about an axis through its center. When the skater's hands and arms are brought in and wrapped around his body to execute the spin, the hands and arms can be considered as a thin-walled, hollow cylinder. His hands and arms have a combined mass 8.0 kg. When outstretched theys pan 1.8 m; when wrapped, they form a cylinder of raduius 25.0 cm. The moment of inertia about the rotation axis of the reminder of his body is constant and equal to 0.40 kg.m2. If the original angular speed is 0.40 rev/s, What is his final angular speed?
 | 
Linear Mode
