An empty office chair is at rest on a floor. consider the following forces: . 1. a downward force due to gravity; . 2. an upward force exerted by the floor; and. 3. a net downward force exerted by the air. which force(s) act on the office chair? . 1. none of the forces act on the chair since. it is at rest. 2. all three forces. 3. 1 only. 4. 1 and 2 only. 5. 2 and 3 only.

What is the energy of a photon of ultraviolet radiation with a frequency of 4.4 × 1015 hz? planck’s constant is 6.63 × 10–34

Photoelectrons with a maximum speed of 6.50 x 107 m/s are ejected from a surface in the presence of light with a frequency of 6.75 x 1014hz. if the mass of an electron is 9.10 x 10-31 kg, calculate in joules the maximum kinetic energy of a single electron. 3.84 x 10-15 j 1.92 x 10-15 j 5.92 x 10-23 j 3.07 x 10-16 j

30 points - when can a theory be modified if a new type of technology allows for new observations that raise new questions? a. immediately, while the questions about the theory are being asked b. after new hypotheses related to the theory are tested in experiments c. only after the new observations disprove all parts of the theory d. while scientists begin to think about how the theory could improve