A 1200 kg truck is moving to the right at a speed of 30 m/s. It hits another identical truck that was at rest. The two trucks stick together and move to the right at a speed of 15 m/s. Elastic: m1 v1B + m2 v2B = m1 v1A + m2 v2A Inelastic: mv1B + mv2B = (m1 + m2 ) Vf a. Is this an elastic or inelastic collidion b. What is the total momentum before the trucks collided with each other? c. What is the total momentum after the trucks collide with each other? Hint: be sure to add both masses then multiply by the velocity. d. Was momentum conserved and how do you know?

When an object is heated it contracts. a. true b. false

Some material consisting of a collection of microscopic objects is kept at a high temperature. a photon detector capable of detecting photon energies from infrared through ultraviolet observes photons emitted with energies of 0.3 ev, 0.5 ev, 0.8 ev, 2.0ev, 2.5ev, and 2.8ev. these are the only photon energies observed. (a) draw and label a possible energy-level diagram for one of the microscopic objects, which has four bound states. on the diagram, indicate the transitions corresponding to the emitted photons. explain briefly. (b) would a spring–mass model be a good model for these microscopic objects? why or why not? (c) the material is now cooled down to a very low temperature, and the photon detector stops detecting photon emissions. next, a beam of light with a continuous range of energies from infrared through ultraviolet shines on the material, and the photon detector observes the beam of light after it passes through the material. what photon energies in this beam of light are observed to be significantly reduced in intensity (“dark absorption lines”)? explain briefly.

Imagine that you have two balloons (or, better yet, actually inflate two balloons, if possible). create static electricity around one of the balloons by rubbing it against your hair or your sweater and then bring that balloon close to the other balloon, which has not been charged. try this with at least one other object—and for variety in the discussion, avoid using an object already described by your classmates. then, for your initial post to the discussion, answer the following questions: what happened with the two balloons?