Physics 200 Homework 1, Part Two Due at the end of class, Wed Sept 16th Don't forget to complete Part One, on Canvast! 1. Reflection on the on-line homework Please write 2-3 sentences for each of the questions. (a) Collisions. Summarize the lessons about energy, momentum and collisions that the on-line homework questions helped you review. (b) The speed of light. Describe in your own words the approach that astronomer Ole Romer took to predict exact times of Io's eclipses. 2. Space-time diagrams A space-time diagram is one where one axis is a direction (say, the x-direction) and one axis is time. We will put the x-direction on the horizontal axis and time on the vertical axis, with the time axis pointing up. The motion of an object can be represented on this diagram with a line. In this question, you will draw a space-time diagram for two children and a ball they are rolling between them. You might find it easier to do this using graph paper. Don't forget to label everything. (a) Jacob and Emily sit 6 meters apart. Let's take Jacob to be at x = 0 and Emily at x=6m. At t=0, Jacob pushes a ball towards Emily with speed of 3m/s and Emily catches it once it reaches her. Emily then immediatelly returs the ball to Jacob at the same speed. He then immediatelly passes it back to her. On a spacetime diagram, plot trajectories corresponding to Jacob, Emily and the ball pass- ing between them (Jacob->Emily->Jacob->Emily) (b) Anne cruises by on her skateboard moving with speed 1m/s in the negative x di- rection. Redraw the whole diagram from part (a) in Anne's reference frame. Assume that Anne was at x=0 at t=0. Turn over for one more question ... 1
3. Interstellar trip When solving this question, assume that all physics is non-relativistic: everything is in- variant under the Galilean transformation and light moves with speed c with respect to an Ether. Assume the Sun and the alien star are motionless with respect to the Ether. A light year is the distance that light travels in one year. If you keep all your distances in light years, it will be much easier to deal with the numbers. For example, a ship travelling at 0.8c needs 12.5 years to travel 10 light years. In the year 3000, humanity sends an exploratory spaceship to a distant star, 100 light years away. The spaceship travels at 0.8c. At the same time as the spaceship is launched, a radio message is sent to the star with information about humanity and the mission. It turns out that an alien civilization occupies the distant solar system. Upon receiving the message, the alien civilization immediatelly sends a radio message to the humanity's spaceship, and then prepares their own spaceship and launches it at 0.6c, 5 years after they receive humanity's message. a) Draw a spacetime diagram showing our solar system, the alien solar system, the two message beams and the two