4. Dr. Sayer is studying how our perceptions of attractiveness have changed over time. He hypothesized that, due to increased concerns over skin cancer, tan skin is perceived as less attractive now than it was 20 years
ago. He compared data from 1987 to current data and found that, on average, tan skin was rated as 4.2 in
attractiveness (on a scale of 1-5, with 5 being most attractive) in 1987 as compared to 3.7 today. In
analyzing these results, what three factors must Dr. Sayer consider when determining if these averages are
reliable?

Two identical small charged spheres are a certain distance apart, and each one initially experiences an electrostatic force of magnitude f due to the other. with time, charge gradually leaks off of both spheres. when each of the spheres has lost half its initial charge, the magnitude of the electrostatic force will be

A23 kg log of wood begins from rest, 300 m up a sluice (a water track used to transport logs, think of it as an inclined plane with negligible friction) inclined at 20° to the horizontal. after it reaches the flat waterway at the bottom it collides elastically with a 100 kg block of wood initially at rest near the base of the incline. (a) how long does it take the 23 kg log to travel down the incline? (b) what is the speed of the 23 kg log at the bottom of the incline? (c) what are the velocities of both blocks of wood after the collision? (d) what is the total kinetic energy before the collision? (e) what is the kinetic energy of the 23 kg log after the collision? (f) what is the kinetic energy of the 100 kg block of wood after the collision? (g) what is the total kinetic energy after the collision? (h) compare the total initial and total final kinetic energies. is this consistent with what you would expect for elastic collisions? explain!

Science and technology are interdependent. advances in one lead to advances in the other. give an example of this phenomenon.