A helicopter has a large main rotor that rotates in a horizontal plane and provides lift. On many helicopters there is a small rotor on the tail that rotates in the vertical plane. Why do helicopters need the small vertical rotor? (Hint: consider what happens when the pilot changes the angular velocity of the main rotor.)
Young and Freedman 10-53:
Figure 10-44 on p.324 of the text shows three identical yo-yos initially at rest on a horizontal surface. For each yo-yo the string is pulled in the direction shown. In each case there is sufficient friction for the yo-yo to roll without slipping. Draw the free-body diagram for each yo-yo. In what direction will each yo-yo rotate?
I go through spurts of travelling extensively for my research. Consequently, it catches my attention when I hear of engines falling off jet airplanes. It happens with a surprisingly high frequency. How can an airplane be in such poor shape that the engine falls off? It turns out that engines are held onto airplanes with breakaway bolts. In certain catastrophic engine failures, these bolts will snap and the engine will fall off the airplane … by design. Why is it necessary to design such a feature into commercial aircraft?
Young and Freedman 10-57:
A block with mass m=5.00 kg slides down a surface inclined 36.9 degrees to the horizontal (see figure 10-47 on page 325 of the text). The coefficient of kinetic friction is 0.25. A string attached to the block is wrapped around a flywheel on a fixed axis through its center. The flywheel has mass 20.0 kg, radius R=0.200 m, and a moment of inertia with respect to the axis 0.400 kg-m2. a) What is the acceleration of the block down the plane? b) What is the tension in the string?
The pilot of a propeller-driven airplane decides to descend abruptly. The propeller is at the front of the airplane and rotates clockwise as seen by the pilot. She lowers the nose of the airplane from a horizontal attitude to one in which the nose is pointed well below the horizontal. As she does this, the nose of the airplane also swings to the left (as seen by the pilot). Explain why this happens. (hint: think about the cause of precession)
You can probably stand flatfooted on the floor, then rise up and balance on your tiptoes. Why can't you do it if your toes are touching the wall of the room? (Try it!)
Young and Freedman 11-4: Two people are carrying a uniform horizontal ladder that is 6.00 m long and weighs 400 N. If one person applies an upward force equal to 180 N at one end, at what point does the other person lift?
If time -
Young and Freedman 11-9:
A diving board 3.00 m long is supported at a point 1.00 m from the end, and a diver weighing 580 N stands at the free end (see figure 11-22 on page 348 in the text). The diving board is of uniform cross section and weighs 320 N. Find a) the force at the support point; b) the force at the end that is held down.