Two ice skaters, of mass 30 kg and 80 kg, are skating across the surface of a frozen lake on a
collision course, with respective velocities of 2.0 m/s in a general north direction, and 1.0 m/s
generally west, as shown above. After they collide, the pair of skaters move off in a direction
north of west with a momentum of approximately 100 kg m/s. How much kinetic energy was
lost in the collision?
OJ
110)
55
70)
120

Follow these directions and answer the questions. 1. set up the ripple tank as in previous investigations. 2. bend the rubber tube to form a "concave mirror" and place in the ripple tank. the water level must be below the top of the hose. 3. generate a few straight pulses with the dowel and observe the reflected waves. do the waves focus (come together) upon reflection? can you locate the place where the waves meet? 4. touch the water surface where the waves converged. what happens to the reflected wave? 5. move your finger twice that distance from the hose (2f = c of c, center of the curvature) and touch the water again. does the image (the reflected wave) appear in the same location (c of c)? you may have to experiment before you find the exact location. sometimes it is hard to visualize with the ripple tank because the waves move so quickly. likewise, it is impossible to "see" light waves because they have such small wavelengths and move at the speed of light. however, both are examples of transverse waves and behave in the same way when a parallel wave fronts hit a curved surface.

Consider an insulating crystal, made up of layers of atoms. what form would you expect the temperature dependence of the phonon heat capacity to approach at extremely low temperatures if the interlayer coupling is i)very strong (rigid coupling), and ii) very weak. explain.

Language is not the only way that humans communicate. describe how we use sound, touch, chemicals, and sight to communicate. need answer asap